• Community
• Technological values - particularly, compared to C/C++
  • Ostensible values
  • Attitude to the programmer s mistakes
  • The ideology of the hardcore programmer
  • Memory safety as a power struggle
  • Memory safety via Rust as a power struggle
• Notes
  • This is not a RIIR manifesto
  • Disclosure
  • On the meaning of woke
• Pithy conclusion

A language empowering everyone to build reliable and efficient software.

Changes in version 0.1.7 (2025-03-22)

• The CI setup was updated to use run.sh from r-ci (Dirk).
• The windows build was updated to GSL 2.7, and UCRT support was added (Jeroen in #16).
• Manual pages now use JSS DOIs for references per CRAN request
• README.md links and badges have been updated
• Continuous integration actions have been updated several times
• The DESCRIPTION file now uses Authors@R as mandated
• Use of multiple cores is eased via a new helper function reflecting option mc.core or architecture defaults, used in tests
• An inline function has been added to avoid a compiler nag
• Support for exponential RNG draws zrexp has been added, the internal uniform generator is now also exposed via zruni
• The vignette bibliography has been updated, and switched to DOIs
• New package zigg is now mentioned in DESCRIPTION and vignette

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. If you like this or other open-source work I do, you can sponsor me at GitHub.

Background When defining a function recursively in Lean that has nested recursion, e.g. a recusive call that is in the argument to a higher-order function like List.map, then extra attention used to be necessary so that Lean can see that xs.map applies its argument only elements of the list xs. The usual idiom is to write xs.attach.map instead, where List.attach attaches to the list elements a proof that they are in that list. You can read more about this my Lean blog post on recursive definitions and our new shiny reference manual, look for Example Nested Recursion in Higher-order Functions . To make this step less tedious I taught Lean to automatically rewrite xs.map to xs.attach.map (where suitable) within the construction of well-founded recursion, so that nested recursion just works (issue #5471). We already do such a rewriting to change if c then else to the dependent if h : c then else , but the attach-introduction is much more ambitious (the rewrites are not definitionally equal, there are higher-order arguments etc.) Rewriting the terms in a way that we can still prove the connection later when creating the equational lemmas is hairy at best. Also, we want the whole machinery to be extensible by the user, setting up their own higher order functions to add more facts to the context of the termination proof. I implemented it like this (PR #6744) and it ships with 4.18.0, but in the course of this work I thought about a quite different and maybe better way to do this, and well-founded recursion in general:

A simpler fix Recall that to use WellFounded.fix

WellFounded.fix : (hwf : WellFounded r) (F : (x :  )   ((y :  )   r y x   C y)   C x) (x :  ) : C x

we have to rewrite the functorial of the recursive function, which naturally has type

F : ((y :  )    C y)   ((x :  )   C x)

to the one above, where all recursive calls take the termination proof r y x. This is a fairly hairy operation, mangling the type of matcher s motives and whatnot. Things are simpler for recursive definitions using the new partial_fixpoint machinery, where we use Lean.Order.fix

Lean.Order.fix : [CCPO  ] (F :      ) (hmono : monotone F) :  

so the functorial s type is unmodified (here will be ((x : ) C x)), and everything else is in the propositional side-condition montone F. For this predicate we have a syntax-guided compositional tactic, and it s easily extensible, e.g. by

theorem monotone_mapM (f :         m  ) (xs : List  ) (hmono : monotone f) :
    monotone (fun x => xs.mapM (f x)) 

Once given, we don t care about the content of that proof. In particular proving the unfolding theorem only deals with the unmodified F that closely matches the function definition as written by the user. Much simpler!

Isabelle has it easier Isabelle also supports well-founded recursion, and has great support for nested recursion. And it s much simpler! There, all you have to do to make nested recursion work is to define a congruence lemma of the form, for List.map something like our List.map_congr_left

List.map_congr_left : (h :   a   l, f a = g a) :
    List.map f l = List.map g l

This is because in Isabelle, too, the termination proofs is a side-condition that essentially states the functorial F calls its argument f only on smaller arguments .

Can we have it easy, too? I had wished we could do the same in Lean for a while, but that form of congruence lemma just isn t strong enough for us. But maybe there is a way to do it, using an existential to give a witness that F can alternatively implemented using the more restrictive argument. The following callsOn P F predicate can express that F calls its higher-order argument only on arguments that satisfy the predicate P:

section setup
variable   : Sort u 
variable   :     Sort v 
variable   : Sort w 
def callsOn (P :     Prop) (F : (  y,   y)    ) :=
    (F': (  y, P y     y)    ),   f, F' (fun y _ => f y) = F f
variable (R :         Prop)
variable (F : (  y,   y)   (  x,   x))
local infix:50 "   " => R
def recursesVia : Prop :=   x, callsOn (    x) (fun f => F f x)
noncomputable def fix (wf : WellFounded R) (h : recursesVia R F) : (  x,   x) :=
  wf.fix (fun x => (h x).choose)
def fix_eq (wf : WellFounded R) h x :
    fix R F wf h x = F (fix R F wf h) x := by
  unfold fix
  rw [wf.fix_eq]
  apply (h x).choose_spec

This allows nice compositional lemmas to discharge callsOn predicates:

theorem callsOn_base (y :  ) (hy : P y) :
    callsOn P (fun (f :   x,   x) => f y) := by
  exists fun f => f y hy
  intros; rfl
@[simp]
theorem callsOn_const (x :  ) :
    callsOn P (fun (_ :   x,   x) => x) :=
   fun _ => x, fun _ => rfl 
theorem callsOn_app
      : Sort uu    : Sort ww 
    (F  :  (  y,   y)        ) -- can this also support dependent types?
    (F  :  (  y,   y)    )
    (h  : callsOn P F )
    (h  : callsOn P F ) :
    callsOn P (fun f => F  f (F  f)) := by
  obtain  F ', h  := h 
  obtain  F ', h  := h 
  exists (fun f => F ' f (F ' f))
  intros; simp_all
theorem callsOn_lam
      : Sort uu 
    (F :     (  y,   y)    ) -- can this also support dependent types?
    (h :   x, callsOn P (F x)) :
    callsOn P (fun f x => F x f) := by
  exists (fun f x => (h x).choose f)
  intro f
  ext x
  apply (h x).choose_spec
theorem callsOn_app2
      : Sort uu    : Sort ww 
    (g :          )
    (F  :  (  y,   y)    ) -- can this also support dependent types?
    (F  :  (  y,   y)    )
    (h  : callsOn P F )
    (h  : callsOn P F ) :
    callsOn P (fun f => g (F  f) (F  f)) := by
  apply_rules [callsOn_app, callsOn_const]

With this setup, we can have the following, possibly user-defined, lemma expressing that List.map calls its arguments only on elements of the list:

theorem callsOn_map (  : Type uu) (  : Type ww)
    (P :     Prop) (F : (  y,   y)        ) (xs : List  )
    (h :   x, x   xs   callsOn P (fun f => F f x)) :
    callsOn P (fun f => xs.map (fun x => F f x)) := by
  suffices callsOn P (fun f => xs.attach.map (fun  x, h  => F f x)) by
    simpa
  apply callsOn_app
    apply callsOn_app
      apply callsOn_const
      apply callsOn_lam
      intro  x', hx' 
      dsimp
      exact (h x' hx')
    apply callsOn_const
end setup

So here is the (manual) construction of a nested map for trees:

section examples
structure Tree (  : Type u) where
  val :  
  cs : List (Tree  )
-- essentially
-- def Tree.map (f :      ) : Tree     Tree   :=
--   fun t =>  f t.val, t.cs.map Tree.map )
noncomputable def Tree.map (f :      ) : Tree     Tree   :=
  fix (sizeOf   < sizeOf  ) (fun map t =>  f t.val, t.cs.map map )
    (InvImage.wf (sizeOf  ) WellFoundedRelation.wf) <  by
  intro  v, cs 
  dsimp only
  apply callsOn_app2
    apply callsOn_const
    apply callsOn_map
    intro t' ht'
    apply callsOn_base
    -- ht' : t'   cs -- !
    --   sizeOf t' < sizeOf   val := v, cs := cs  
    decreasing_trivial
end examples

This makes me happy! All details of the construction are now contained in a proof that can proceed by a syntax-driven tactic and that s easily and (likely robustly) extensible by the user. It also means that we can share a lot of code paths (e.g. everything related to equational theorems) between well-founded recursion and partial_fixpoint. I wonder if this construction is really as powerful as our current one, or if there are certain (likely dependently typed) functions where this doesn t fit, but the above is dependent, so it looks good. With this construction, functions defined by well-founded recursion will reduce even worse in the kernel, I assume. This may be a good thing.

The cake is a lie What unfortunately kills this idea, though, is the generation of the functional induction principles, which I believe is not (easily) possible with this construction: The functional induction principle is proved by massaging F to return a proof, but since the extra assumptions (e.g. for ite or List.map) only exist in the termination proof, they are not available in F. Oh wey, how anticlimactic.

PS: Path dependencies Curiously, if we didn t have functional induction at this point yet, then very likely I d change Lean to use this construction, and then we d either not get functional induction, or it would be implemented very differently, maybe a more syntactic approach that would re-prove termination. I guess that s called path dependence.

• El d a despu s de la cat strofe: Bah a volvi a amanecer destrozada, La Nueva.
• En 20 im genes, el inmenso da o que provoc el temporal en Bah a, La Nueva.
• Drone footage of the nearby stream, which now seems a river, Instagram.
• Drone footage of the same above stream nearer the golf club and entering the city - MP4. I do not know the author, happy to give the proper credits if contacted!!!

• NVidia specs lie
• My 8K cable isn t really an 8K cable
• Something weird happens converting DisplayPort to HDMI
• The video card can only handle refresh rates for 8K that don t match supported input for the TV

• [1] https://etbe.coker.com.au/2024/12/15/hisense-65u80g-8k-tv/
• [2] https://tinyurl.com/2cr32835
• [3] https://en.wikipedia.org/wiki/DisplayPort
• [4] https://en.wikipedia.org/wiki/Display_Stream_Compression
• [5] https://lemmy.ml/post/26711723
• [6] https://www.techpowerup.com/gpu-specs/arc-b580.c4244

• We are trying to put together a schedule for one week
• Each day has some set of work shifts that need to be staffed
• Each shift must be staffed with exactly one worker
• The shift schedule is known beforehand, and the workers each declare their preferences beforehand: they mark each shift in the week as one of:
  • PREFERRED (if they want to be scheduled on that shift)
  • NEUTRAL
  • DISFAVORED (if they don't love that shift)
  • REFUSED (if they absolutely cannot work that shift)

#!/usr/bin/python3
import sys
import os
import re
def report_solution_to_console(vars):
    for w in days_of_week:
        annotation = ''
        if human_annotate is not None:
            for s in shifts.keys():
                m = re.match(rf' w  - ', s)
                if not m: continue
                if vars[human_annotate][s].value():
                    annotation = f" ( human_annotate  SCHEDULED)"
                    break
            if not len(annotation):
                annotation = f" ( human_annotate  OFF)"
        print(f" w annotation ")
        for s in shifts.keys():
            m = re.match(rf' w  - ', s)
            if not m: continue
            annotation = ''
            if human_annotate is not None:
                annotation = f" ( human_annotate   shifts[s][human_annotate] )"
            print(f"    ----  s[m.end():] annotation ")
            for h in humans:
                if vars[h][s].value():
                    print(f"          h  ( shifts[s][h] )")
def report_solution_summary_to_console(vars):
    print("\nSUMMARY")
    for h in humans:
        print(f"--  h ")
        print(f"   benefit:  benefits[h].value():.3f ")
        counts = dict()
        for a in availabilities:
            counts[a] = 0
        for s in shifts.keys():
            if vars[h][s].value():
                counts[shifts[s][h]] += 1
        for a in availabilities:
            print(f"    counts[a]   a ")
human_annotate = None
days_of_week = ('SUNDAY',
                'MONDAY',
                'TUESDAY',
                'WEDNESDAY',
                'THURSDAY',
                'FRIDAY',
                'SATURDAY')
humans = ['ALICE', 'BOB',
          'CAROL', 'DAVID', 'EVE', 'FRANK', 'GRACE', 'HEIDI', 'IVAN', 'JUDY']
shifts =  'SUNDAY - SANDING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'DISFAVORED',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'JUDY':  'NEUTRAL' ,
          'WEDNESDAY - SAWING 7:30 AM - 2:30 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'EVE':   'REFUSED',
           'JUDY':  'REFUSED' ,
          'THURSDAY - SANDING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'PREFERRED',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED' ,
          'SATURDAY - SAWING 7:30 AM - 2:30 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'FRANK': 'PREFERRED',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'EVE':   'REFUSED',
           'JUDY':  'REFUSED',
           'GRACE': 'REFUSED' ,
          'SUNDAY - SAWING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED' ,
          'MONDAY - SAWING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'PREFERRED',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED' ,
          'TUESDAY - SAWING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'NEUTRAL',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED' ,
          'WEDNESDAY - PAINTING 7:30 AM - 2:30 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'EVE':   'REFUSED',
           'JUDY':  'REFUSED',
           'DAVID': 'REFUSED' ,
          'THURSDAY - SAWING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'PREFERRED',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED' ,
          'FRIDAY - SAWING 9:00 AM - 4:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'DAVID': 'PREFERRED',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'PREFERRED',
           'IVAN':  'PREFERRED',
           'JUDY':  'DISFAVORED',
           'HEIDI': 'REFUSED' ,
          'SATURDAY - PAINTING 7:30 AM - 2:30 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'FRANK': 'PREFERRED',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'EVE':   'REFUSED',
           'JUDY':  'REFUSED',
           'GRACE': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'SUNDAY - PAINTING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'MONDAY - PAINTING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'PREFERRED',
           'IVAN':  'PREFERRED',
           'JUDY':  'NEUTRAL',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'TUESDAY - PAINTING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'NEUTRAL',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'WEDNESDAY - SANDING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'DAVID': 'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'JUDY':  'NEUTRAL',
           'EVE':   'REFUSED' ,
          'THURSDAY - PAINTING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'NEUTRAL',
           'IVAN':  'PREFERRED',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'FRIDAY - PAINTING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'PREFERRED',
           'FRANK': 'PREFERRED',
           'GRACE': 'PREFERRED',
           'IVAN':  'PREFERRED',
           'JUDY':  'DISFAVORED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'SATURDAY - SANDING 9:45 AM - 4:45 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'DAVID': 'PREFERRED',
           'FRANK': 'PREFERRED',
           'HEIDI': 'DISFAVORED',
           'IVAN':  'PREFERRED',
           'EVE':   'REFUSED',
           'JUDY':  'REFUSED',
           'GRACE': 'REFUSED' ,
          'SUNDAY - PAINTING 11:00 AM - 6:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'PREFERRED',
           'IVAN':  'NEUTRAL',
           'JUDY':  'NEUTRAL',
           'DAVID': 'REFUSED' ,
          'MONDAY - PAINTING 12:00 PM - 7:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'PREFERRED',
           'IVAN':  'NEUTRAL',
           'JUDY':  'NEUTRAL',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'TUESDAY - PAINTING 12:00 PM - 7:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'NEUTRAL',
           'HEIDI': 'REFUSED',
           'JUDY':  'REFUSED',
           'DAVID': 'REFUSED' ,
          'WEDNESDAY - PAINTING 12:00 PM - 7:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'NEUTRAL',
           'JUDY':  'PREFERRED',
           'EVE':   'REFUSED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'THURSDAY - PAINTING 12:00 PM - 7:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'NEUTRAL',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'FRIDAY - PAINTING 12:00 PM - 7:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'NEUTRAL',
           'JUDY':  'DISFAVORED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'SATURDAY - PAINTING 12:00 PM - 7:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'NEUTRAL',
           'FRANK': 'NEUTRAL',
           'IVAN':  'NEUTRAL',
           'JUDY':  'DISFAVORED',
           'EVE':   'REFUSED',
           'HEIDI': 'REFUSED',
           'GRACE': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'SUNDAY - SAWING 12:00 PM - 7:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'NEUTRAL',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'NEUTRAL',
           'JUDY':  'PREFERRED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'MONDAY - SAWING 2:00 PM - 9:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'TUESDAY - SAWING 2:00 PM - 9:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'HEIDI': 'REFUSED',
           'JUDY':  'REFUSED',
           'DAVID': 'REFUSED' ,
          'WEDNESDAY - SAWING 2:00 PM - 9:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'EVE':   'REFUSED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'THURSDAY - SAWING 2:00 PM - 9:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'HEIDI': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'FRIDAY - SAWING 2:00 PM - 9:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'HEIDI': 'REFUSED',
           'JUDY':  'REFUSED',
           'DAVID': 'REFUSED' ,
          'SATURDAY - SAWING 2:00 PM - 9:00 PM':
           'ALICE': 'PREFERRED',
           'BOB':   'PREFERRED',
           'CAROL': 'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'EVE':   'REFUSED',
           'HEIDI': 'REFUSED',
           'GRACE': 'REFUSED',
           'DAVID': 'REFUSED' ,
          'SUNDAY - PAINTING 12:15 PM - 7:15 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'PREFERRED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'NEUTRAL',
           'DAVID': 'REFUSED' ,
          'MONDAY - PAINTING 2:00 PM - 9:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'DAVID': 'REFUSED' ,
          'TUESDAY - PAINTING 2:00 PM - 9:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'REFUSED',
           'DAVID': 'REFUSED' ,
          'WEDNESDAY - PAINTING 2:00 PM - 9:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'EVE':   'REFUSED',
           'DAVID': 'REFUSED' ,
          'THURSDAY - PAINTING 2:00 PM - 9:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'DAVID': 'REFUSED' ,
          'FRIDAY - PAINTING 2:00 PM - 9:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'DISFAVORED',
           'EVE':   'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'GRACE': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'REFUSED',
           'DAVID': 'REFUSED' ,
          'SATURDAY - PAINTING 2:00 PM - 9:00 PM':
           'ALICE': 'NEUTRAL',
           'BOB':   'NEUTRAL',
           'CAROL': 'DISFAVORED',
           'FRANK': 'NEUTRAL',
           'HEIDI': 'NEUTRAL',
           'IVAN':  'DISFAVORED',
           'JUDY':  'DISFAVORED',
           'EVE':   'REFUSED',
           'GRACE': 'REFUSED',
           'DAVID': 'REFUSED' 
availabilities = ['PREFERRED', 'NEUTRAL', 'DISFAVORED']
import pulp
prob = pulp.LpProblem("Scheduling", pulp.LpMaximize)
vars = pulp.LpVariable.dicts("Assignments",
                             (humans, shifts.keys()),
                             None,None, # bounds; unused, since these are binary variables
                             pulp.LpBinary)
# Everyone works at least 2 shifts
Nshifts_min = 2
for h in humans:
    prob += (
        pulp.lpSum([vars[h][s] for s in shifts.keys()]) >= Nshifts_min,
        f" h  works at least  Nshifts_min  shifts",
    )
# each shift is ~ 8 hours, so I limit everyone to 40/8 = 5 shifts
Nshifts_max = 5
for h in humans:
    prob += (
        pulp.lpSum([vars[h][s] for s in shifts.keys()]) <= Nshifts_max,
        f" h  works at most  Nshifts_max  shifts",
    )
# all shifts staffed and not double-staffed
for s in shifts.keys():
    prob += (
        pulp.lpSum([vars[h][s] for h in humans]) == 1,
        f" s  is staffed",
    )
# each human can work at most one shift on any given day
for w in days_of_week:
    for h in humans:
        prob += (
            pulp.lpSum([vars[h][s] for s in shifts.keys() if re.match(rf' w  ',s)]) <= 1,
            f" h  cannot be double-booked on  w "
        )
#### Some explicit constraints; as an example
# DAVID can't work any PAINTING shift and is off on Thu and Sun
h = 'DAVID'
prob += (
    pulp.lpSum([vars[h][s] for s in shifts.keys() if re.search(r'- PAINTING',s)]) == 0,
    f" h  can't work any PAINTING shift"
)
prob += (
    pulp.lpSum([vars[h][s] for s in shifts.keys() if re.match(r'THURSDAY SUNDAY',s)]) == 0,
    f" h  is off on Thursday and Sunday"
)
# Do not assign any "REFUSED" shifts
for s in shifts.keys():
    for h in humans:
        if shifts[s][h] == 'REFUSED':
            prob += (
                vars[h][s] == 0,
                f" h  is not available for  s "
            )
# Objective. I try to maximize the "happiness". Each human sees each shift as
# one of:
#
#   PREFERRED
#   NEUTRAL
#   DISFAVORED
#   REFUSED
#
# I set a hard constraint to handle "REFUSED", and arbitrarily, I set these
# benefit values for the others
benefit_availability = dict()
benefit_availability['PREFERRED']  = 3
benefit_availability['NEUTRAL']    = 2
benefit_availability['DISFAVORED'] = 1
# Not used, since this is a hard constraint. But the code needs this to be a
# part of the benefit. I can ignore these in the code, but let's keep this
# simple
benefit_availability['REFUSED' ] = -1000
benefits = dict()
for h in humans:
    benefits[h] = \
        pulp.lpSum([vars[h][s] * benefit_availability[shifts[s][h]] \
                    for s in shifts.keys()])
benefit_total = \
    pulp.lpSum([benefits[h] \
                for h in humans])
prob += (
    benefit_total,
    "happiness",
)
prob.solve()
if pulp.LpStatus[prob.status] == "Optimal":
    report_solution_to_console(vars)
    report_solution_summary_to_console(vars)

benefit_availability = dict()
benefit_availability['PREFERRED']  = 3
benefit_availability['NEUTRAL']    = 2
benefit_availability['DISFAVORED'] = 1
benefits = dict()
for h in humans:
    benefits[h] = \
        pulp.lpSum([vars[h][s] * benefit_availability[shifts[s][h]] \
                    for s in shifts.keys()])
benefit_total = \
    pulp.lpSum([benefits[h] \
                for h in humans])

....
Result - Optimal solution found
Objective value:                108.00000000
Enumerated nodes:               0
Total iterations:               0
Time (CPU seconds):             0.01
Time (Wallclock seconds):       0.01
Option for printingOptions changed from normal to all
Total time (CPU seconds):       0.02   (Wallclock seconds):       0.02
SUNDAY
    ---- SANDING 9:00 AM - 4:00 PM
         EVE (PREFERRED)
    ---- SAWING 9:00 AM - 4:00 PM
         IVAN (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM
         FRANK (PREFERRED)
    ---- PAINTING 11:00 AM - 6:00 PM
         HEIDI (PREFERRED)
    ---- SAWING 12:00 PM - 7:00 PM
         ALICE (PREFERRED)
    ---- PAINTING 12:15 PM - 7:15 PM
         CAROL (PREFERRED)
MONDAY
    ---- SAWING 9:00 AM - 4:00 PM
         DAVID (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM
         IVAN (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM
         GRACE (PREFERRED)
    ---- SAWING 2:00 PM - 9:00 PM
         ALICE (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM
         HEIDI (NEUTRAL)
TUESDAY
    ---- SAWING 9:00 AM - 4:00 PM
         DAVID (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM
         EVE (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM
         FRANK (NEUTRAL)
    ---- SAWING 2:00 PM - 9:00 PM
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM
         HEIDI (NEUTRAL)
WEDNESDAY
    ---- SAWING 7:30 AM - 2:30 PM
         DAVID (PREFERRED)
    ---- PAINTING 7:30 AM - 2:30 PM
         IVAN (PREFERRED)
    ---- SANDING 9:45 AM - 4:45 PM
         FRANK (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM
         JUDY (PREFERRED)
    ---- SAWING 2:00 PM - 9:00 PM
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM
         ALICE (NEUTRAL)
THURSDAY
    ---- SANDING 9:00 AM - 4:00 PM
         GRACE (PREFERRED)
    ---- SAWING 9:00 AM - 4:00 PM
         CAROL (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM
         EVE (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM
         JUDY (PREFERRED)
    ---- SAWING 2:00 PM - 9:00 PM
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM
         ALICE (NEUTRAL)
FRIDAY
    ---- SAWING 9:00 AM - 4:00 PM
         DAVID (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM
         FRANK (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM
         GRACE (NEUTRAL)
    ---- SAWING 2:00 PM - 9:00 PM
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM
         HEIDI (NEUTRAL)
SATURDAY
    ---- SAWING 7:30 AM - 2:30 PM
         CAROL (PREFERRED)
    ---- PAINTING 7:30 AM - 2:30 PM
         IVAN (PREFERRED)
    ---- SANDING 9:45 AM - 4:45 PM
         DAVID (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM
         FRANK (NEUTRAL)
    ---- SAWING 2:00 PM - 9:00 PM
         ALICE (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM
         BOB (NEUTRAL)
SUMMARY
-- ALICE
   benefit: 13.000
   3 PREFERRED
   2 NEUTRAL
   0 DISFAVORED
-- BOB
   benefit: 14.000
   4 PREFERRED
   1 NEUTRAL
   0 DISFAVORED
-- CAROL
   benefit: 9.000
   3 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- DAVID
   benefit: 15.000
   5 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- EVE
   benefit: 9.000
   3 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- FRANK
   benefit: 13.000
   3 PREFERRED
   2 NEUTRAL
   0 DISFAVORED
-- GRACE
   benefit: 8.000
   2 PREFERRED
   1 NEUTRAL
   0 DISFAVORED
-- HEIDI
   benefit: 9.000
   1 PREFERRED
   3 NEUTRAL
   0 DISFAVORED
-- IVAN
   benefit: 12.000
   4 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- JUDY
   benefit: 6.000
   2 PREFERRED
   0 NEUTRAL
   0 DISFAVORED

Objective value:                108.00000000
Enumerated nodes:               0
Total iterations:               0
Time (CPU seconds):             0.01
Time (Wallclock seconds):       0.01
Option for printingOptions changed from normal to all
Total time (CPU seconds):       0.01   (Wallclock seconds):       0.02
SUNDAY (JUDY OFF)
    ---- SANDING 9:00 AM - 4:00 PM (JUDY NEUTRAL)
         EVE (PREFERRED)
    ---- SAWING 9:00 AM - 4:00 PM (JUDY PREFERRED)
         IVAN (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM (JUDY PREFERRED)
         FRANK (PREFERRED)
    ---- PAINTING 11:00 AM - 6:00 PM (JUDY NEUTRAL)
         HEIDI (PREFERRED)
    ---- SAWING 12:00 PM - 7:00 PM (JUDY PREFERRED)
         ALICE (PREFERRED)
    ---- PAINTING 12:15 PM - 7:15 PM (JUDY NEUTRAL)
         CAROL (PREFERRED)
MONDAY (JUDY OFF)
    ---- SAWING 9:00 AM - 4:00 PM (JUDY PREFERRED)
         DAVID (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM (JUDY NEUTRAL)
         IVAN (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM (JUDY NEUTRAL)
         GRACE (PREFERRED)
    ---- SAWING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         ALICE (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         HEIDI (NEUTRAL)
TUESDAY (JUDY OFF)
    ---- SAWING 9:00 AM - 4:00 PM (JUDY PREFERRED)
         DAVID (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM (JUDY PREFERRED)
         EVE (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM (JUDY REFUSED)
         FRANK (NEUTRAL)
    ---- SAWING 2:00 PM - 9:00 PM (JUDY REFUSED)
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM (JUDY REFUSED)
         HEIDI (NEUTRAL)
WEDNESDAY (JUDY SCHEDULED)
    ---- SAWING 7:30 AM - 2:30 PM (JUDY REFUSED)
         DAVID (PREFERRED)
    ---- PAINTING 7:30 AM - 2:30 PM (JUDY REFUSED)
         IVAN (PREFERRED)
    ---- SANDING 9:45 AM - 4:45 PM (JUDY NEUTRAL)
         FRANK (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM (JUDY PREFERRED)
         JUDY (PREFERRED)
    ---- SAWING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         ALICE (NEUTRAL)
THURSDAY (JUDY SCHEDULED)
    ---- SANDING 9:00 AM - 4:00 PM (JUDY PREFERRED)
         GRACE (PREFERRED)
    ---- SAWING 9:00 AM - 4:00 PM (JUDY PREFERRED)
         CAROL (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM (JUDY PREFERRED)
         EVE (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM (JUDY PREFERRED)
         JUDY (PREFERRED)
    ---- SAWING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         ALICE (NEUTRAL)
FRIDAY (JUDY OFF)
    ---- SAWING 9:00 AM - 4:00 PM (JUDY DISFAVORED)
         DAVID (PREFERRED)
    ---- PAINTING 9:45 AM - 4:45 PM (JUDY DISFAVORED)
         FRANK (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM (JUDY DISFAVORED)
         GRACE (NEUTRAL)
    ---- SAWING 2:00 PM - 9:00 PM (JUDY REFUSED)
         BOB (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM (JUDY REFUSED)
         HEIDI (NEUTRAL)
SATURDAY (JUDY OFF)
    ---- SAWING 7:30 AM - 2:30 PM (JUDY REFUSED)
         CAROL (PREFERRED)
    ---- PAINTING 7:30 AM - 2:30 PM (JUDY REFUSED)
         IVAN (PREFERRED)
    ---- SANDING 9:45 AM - 4:45 PM (JUDY REFUSED)
         DAVID (PREFERRED)
    ---- PAINTING 12:00 PM - 7:00 PM (JUDY DISFAVORED)
         FRANK (NEUTRAL)
    ---- SAWING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         ALICE (PREFERRED)
    ---- PAINTING 2:00 PM - 9:00 PM (JUDY DISFAVORED)
         BOB (NEUTRAL)
SUMMARY
-- ALICE
   benefit: 13.000
   3 PREFERRED
   2 NEUTRAL
   0 DISFAVORED
-- BOB
   benefit: 14.000
   4 PREFERRED
   1 NEUTRAL
   0 DISFAVORED
-- CAROL
   benefit: 9.000
   3 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- DAVID
   benefit: 15.000
   5 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- EVE
   benefit: 9.000
   3 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- FRANK
   benefit: 13.000
   3 PREFERRED
   2 NEUTRAL
   0 DISFAVORED
-- GRACE
   benefit: 8.000
   2 PREFERRED
   1 NEUTRAL
   0 DISFAVORED
-- HEIDI
   benefit: 9.000
   1 PREFERRED
   3 NEUTRAL
   0 DISFAVORED
-- IVAN
   benefit: 12.000
   4 PREFERRED
   0 NEUTRAL
   0 DISFAVORED
-- JUDY
   benefit: 6.000
   2 PREFERRED
   0 NEUTRAL
   0 DISFAVORED

benefit_boost_Nshifts = \
     2: -0.8,
     3: -0.5,
     4: -0.3,
     5: -0.2 
for h in humans:
    benefits[h] = \
        ... + \
        pulp.lpSum([vars_Nshifts[h][n] * benefit_boost_Nshifts[n] \
                    for n in benefit_boost_Nshifts.keys()])

#!/usr/bin/python3
import numpy as np
import gnuplotlib as gp
Nshifts_eq  = 4
Nshifts_max = 10
Nshifts = np.arange(Nshifts_max+1)
i0 = np.nonzero(Nshifts != Nshifts_eq)[0]
i1 = np.nonzero(Nshifts == Nshifts_eq)[0]
gp.plot( # True value: var_Nshifts4==0, Nshifts!=4
         ( np.zeros(i0.shape),
           Nshifts[i0],
           dict(_with     = 'points pt 7 ps 1 lc "red"') ),
         # True value: var_Nshifts4==1, Nshifts==4
         ( np.ones(i1.shape),
           Nshifts[i1],
           dict(_with     = 'points pt 7 ps 1 lc "red"') ),
         # False value: var_Nshifts4==1, Nshifts!=4
         ( np.ones(i0.shape),
           Nshifts[i0],
           dict(_with     = 'points pt 7 ps 1 lc "black"') ),
         # False value: var_Nshifts4==0, Nshifts==4
         ( np.zeros(i1.shape),
           Nshifts[i1],
           dict(_with     = 'points pt 7 ps 1 lc "black"') ),
        unset=('grid'),
        _set = (f'xtics ("(Nshifts== Nshifts_eq ) == 0" 0, "(Nshifts== Nshifts_eq ) == 1" 1)'),
        _xrange = (-0.1, 1.1),
        ylabel = "Nshifts",
        title = "Nshifts equality variable: not linearly separable",
        hardcopy = "/tmp/scheduling-Nshifts-eq.svg")

#!/usr/bin/python3
import numpy as np
import numpysane as nps
import gnuplotlib as gp
Nshifts_leq = 4
Nshifts_max = 10
Nshifts = np.arange(Nshifts_max+1)
i0 = np.nonzero(Nshifts >  Nshifts_leq)[0]
i1 = np.nonzero(Nshifts <= Nshifts_leq)[0]
def linear_slope_yintercept(xy0,xy1):
    m = (xy1[1] - xy0[1])/(xy1[0] - xy0[0])
    b = xy1[1] - m * xy1[0]
    return np.array(( m, b ))
x01     = np.arange(2)
x01_one = nps.glue( nps.transpose(x01), np.ones((2,1)), axis=-1)
y_lowerbound = nps.inner(x01_one,
                         linear_slope_yintercept( np.array((0, Nshifts_leq+1)),
                                                  np.array((1, 0)) ))
y_upperbound = nps.inner(x01_one,
                         linear_slope_yintercept( np.array((0, Nshifts_max)),
                                                  np.array((1, Nshifts_leq)) ))
y_lowerbound_check = (1-x01) * (Nshifts_leq+1)
y_upperbound_check = Nshifts_max - x01*(Nshifts_max-Nshifts_leq)
gp.plot( # True value: var_Nshifts_leq4==0, Nshifts>4
         ( np.zeros(i0.shape),
           Nshifts[i0],
           dict(_with     = 'points pt 7 ps 1 lc "red"') ),
         # True value: var_Nshifts_leq4==1, Nshifts<=4
         ( np.ones(i1.shape),
           Nshifts[i1],
           dict(_with     = 'points pt 7 ps 1 lc "red"') ),
         # False value: var_Nshifts_leq4==1, Nshifts>4
         ( np.ones(i0.shape),
           Nshifts[i0],
           dict(_with     = 'points pt 7 ps 1 lc "black"') ),
         # False value: var_Nshifts_leq4==0, Nshifts<=4
         ( np.zeros(i1.shape),
           Nshifts[i1],
           dict(_with     = 'points pt 7 ps 1 lc "black"') ),
         ( x01, y_lowerbound, y_upperbound,
           dict( _with     = 'filledcurves lc "green"',
                 tuplesize = 3) ),
         ( x01, nps.cat(y_lowerbound_check, y_upperbound_check),
           dict( _with     = 'lines lc "green" lw 2',
                 tuplesize = 2) ),
        unset=('grid'),
        _set = (f'xtics ("(Nshifts<= Nshifts_leq ) == 0" 0, "(Nshifts<= Nshifts_leq ) == 1" 1)',
                'style fill transparent pattern 1'),
        _xrange = (-0.1, 1.1),
        ylabel = "Nshifts",
        title = "Nshifts inequality variable: linearly separable",
        hardcopy = "/tmp/scheduling-Nshifts-leq.svg")

# I want to favor people getting more extra shifts at the start to balance
# things out: somebody getting one more shift on their pile shouldn't take
# shifts away from under-utilized people
benefit_boost_leq_bound = \
     2: .2,
     3: .3,
     4: .4,
     5: .5 
# Constrain vars_Nshifts_leq variables to do the right thing
for h in humans:
    for b in benefit_boost_leq_bound.keys():
        prob += (pulp.lpSum([vars[h][s] for s in shifts.keys()])
                 >= (1 - vars_Nshifts_leq[h][b])*(b+1),
                 f" h  at least  b  shifts: lower bound")
        prob += (pulp.lpSum([vars[h][s] for s in shifts.keys()])
                 <= Nshifts_max - vars_Nshifts_leq[h][b]*(Nshifts_max-b),
                 f" h  at least  b  shifts: upper bound")
benefits = dict()
for h in humans:
    benefits[h] = \
        ... + \
        pulp.lpSum([vars_Nshifts_leq[h][b] * benefit_boost_leq_bound[b] \
                    for b in benefit_boost_leq_bound.keys()])

Comparison of architecture and mainstream adoption potential

Protocol	Identity System	Example	Storage model	Cost for end users	Potential
Mastodon	Tied to server domain	@ottok@mastodon.social	Federated instances	Free (some instances charge)	High
Bluesky	Portable (DID)	ottoke.bsky.social	Federated instances	Free	Moderate
Farcaster	ENS (Ethereum)	@ottok	Blockchain + off-chain	Small gas fees	Moderate
Lens	NFT-based (Polygon)	@ottok	Blockchain + off-chain	Small gas fees	Niche
Nostr	Cryptographic Keys	npub16lc6uhqpg6dnqajylkhwuh3j7ynhcnje508tt4v6703w9kjlv9vqzz4z7f	Federated instances	Free (some instances charge)	Niche

1. Mastodon (ActivityPub) Mastodon was created in 2016 by Eugen Rochko, a German software developer who sought to provide a decentralized and user-controlled alternative to Twitter. It was built on the ActivityPub protocol, now standardized by W3C Social Web Working Group, to allow users to join independent servers while still communicating across the broader Mastodon network. Mastodon operates on a federated model, where multiple independently run servers communicate via ActivityPub. Each server sets its own moderation policies, leading to a decentralized but fragmented experience. The servers can alternatively be called instances, relays or nodes, depending on what vocabulary a protocol has standardized on.

• Identity: User identity is tied to the instance where they registered, represented as @username@instance.tld.
• Storage: Data is stored on individual instances, which federate messages to other instances based on their configurations.
• Cost: Free to use, but relies on instance operators willing to run the servers.

The protocol defines multiple activities such as:

• Creating a post
• Liking
• Sharing
• Following
• Commenting

Example Message in ActivityPub (JSON-LD Format)

json Copy

"@context": "https://www.w3.org/ns/activitystreams", "type": "Create", "actor": "https://mastodon.social/users/ottok", "object": "type": "Note", "content": "Hello from #Mastodon!", "published": "2025-03-03T12:00:00Z", "to": ["https://www.w3.org/ns/activitystreams#Public"]

 
 "@context": "https://www.w3.org/ns/activitystreams",
 "type": "Create",
 "actor": "https://mastodon.social/users/ottok",
 "object":  
 "type": "Note",
 "content": "Hello from #Mastodon!",
 "published": "2025-03-03T12:00:00Z",
 "to": ["https://www.w3.org/ns/activitystreams#Public"]
  
 

Servers communicate across different platforms by publishing activities to their followers or forwarding activities between servers. Standard HTTPS is used between servers for communication, and the messages use JSON-LD for data representation. The WebFinger protocol is used for user discovery. There is however no neat way for home server discovery yet. This means that if you are browsing e.g. Fosstodon and want to follow a user and press Follow, a dialog will pop up asking you to enter your own home server (e.g. mastodon.social) to redirect you there for actually executing the Follow action on with your account. Mastodon is open source under the AGPL at github.com/mastodon/mastodon. Anyone can operate their own instance. It just requires to run your own server and some skills to maintain a Ruby on Rails app with a PostgreSQL database backend, and basic understanding of the protocol to configure federation with other ActivityPub instances.

Popularity: Already established, but will it grow more? Mastodon has seen steady growth, especially after Twitter s acquisition in 2022, with some estimates stating it peaked at 10 million users across thousands of instances. However, its fragmented user experience and the complexity of choosing instances have hindered mainstream adoption. Still, it remains the most established decentralized alternative to Twitter. Note that Donald Trump s Truth Social is based on the Mastodon software but does not federate with the ActivityPub network. The ActivityPub protocol is the most widely used of its kind. One of the other most popular services is the Lemmy link sharing service, similar to Reddit. The larger ecosystem of ActivityPub is called Fediverse, and estimates put the total active user count around 6 million.

2. Bluesky (AT Protocol) Interestingly, Bluesky was conceived within Twitter in 2019 by Twitter founder Jack Dorsey. After being incubated as a Twitter-funded project, it spun off as an independent Public Benefit LLC in February 2022 and launched its public beta in February 2023. Bluesky runs on top of the Authenticated Transfer (AT) Protocol published at https://github.com/bluesky-social/atproto. The protocol enables portable identities and data ownership, meaning users can migrate between platforms while keeping their identity and content intact. In practice, however, there is only one popular server at the moment, which is Bluesky itself.

• Identity: Usernames are domain-based (e.g., @user.bsky.social).
• Storage: Content is theoretically federated among various servers.
• Cost: Free to use, but relies on instance operators willing to run the servers.

Example Message in AT Protocol (JSON Format)

json Copy

"repo": "did:plc:ottoke.bsky.social", "collection": "app.bsky.feed.post", "record": "$type": "app.bsky.feed.post", "text": "Hello from Bluesky!", "createdAt": "2025-03-03T12:00:00Z", "langs": ["en"]

 
 "repo": "did:plc:ottoke.bsky.social",
 "collection": "app.bsky.feed.post",
 "record":  
 "$type": "app.bsky.feed.post",
 "text": "Hello from Bluesky!",
 "createdAt": "2025-03-03T12:00:00Z",
 "langs": ["en"]
  
 

Popularity: Hybrid approach may have business benefits? Bluesky reported over 3 million users by 2024, probably getting traction due to its Twitter-like interface and Jack Dorsey s involvement. Its hybrid approach decentralized identity with centralized components could make it a strong candidate for mainstream adoption, assuming it can scale effectively.

3. Warpcast (Farcaster Network) Farcaster was launched in 2021 by Dan Romero and Varun Srinivasan, both former crypto exchange Coinbase executives, to create a decentralized but user-friendly social network. Built on the Ethereum blockchain, it could potentially offer a very attack-resistant communication medium. However, in my own testing, Farcaster does not seem to fully leverage what Ethereum could offer. First of all, there is no diversity in programs implementing the protocol as at the moment there is only Warpcast. In Warpcast the signup requires an initial 5 USD fee that is not payable in ETH, and users need to create a new wallet address on the Ethereum layer 2 network Base instead of simply reusing their existing Ethereum wallet address or ENS name. Despite this, I can understand why Farcaster may have decided to start out like this. Having a single client program may be the best strategy initially. One of the decentralized chat protocol Matrix founders, Matthew Hodgson, shared in his FOSDEM 2025 talk that he slightly regrets focusing too much on developing the protocol instead of making sure the app to use it is attractive to end users. So it may be sensible to ensure Warpcast gets popular first, before attempting to make the Farcaster protocol widely used. As a protocol Farcaster s hybrid approach makes it more scalable than fully on-chain networks, giving it a higher chance of mainstream adoption if it integrates seamlessly with broader Web3 ecosystems.

• Identity: ENS (Ethereum Name Service) domains are used as usernames.
• Storage: Messages are stored in off-chain hubs, while identity is on-chain.
• Cost: Users must pay gas fees for some operations but reading and posting messages is mostly free.

Example Message in Farcaster (JSON Format)

json Copy

"fid": 766579, "username": "ottok", "custodyAddress": "0x127853e48be3870172baa4215d63b6d815d18f21", "connectedWallet": "0x3ebe43aa3ae5b891ca1577d9c49563c0cee8da88", "text": "Hello from Farcaster!", "publishedAt": 1709424000, "replyTo": null, "embeds": []

 
 "fid": 766579,
 "username": "ottok",
 "custodyAddress": "0x127853e48be3870172baa4215d63b6d815d18f21",
 "connectedWallet": "0x3ebe43aa3ae5b891ca1577d9c49563c0cee8da88",
 "text": "Hello from Farcaster!",
 "publishedAt": 1709424000,
 "replyTo": null,
 "embeds": []
 

Popularity: Decentralized social media + decentralized payments a winning combo? Ethereum founder Vitalik Buterin (warpcast.com/vbuterin) and many core developers are active on the platform. Warpcast, the main client for Farcaster, has seen increasing adoption, especially among Ethereum developers and Web3 enthusiasts. I too have an profile at warpcast.com/ottok. However, the numbers are still very low and far from reaching network effects to really take off. Blockchain-based social media networks, particularly those built on Ethereum, are compelling because they leverage existing user wallets and persistent identities while enabling native payment functionality. When combined with decentralized content funding through micropayments, these blockchain-backed social networks could offer unique advantages that centralized platforms may find difficult to replicate, being decentralized both as a technical network and in a funding mechanism.

4. Hey.xyz (Lens Network) The Lens Protocol was developed by decentralized finance (DeFi) team Aave and launched in May 2022 to provide a user-owned social media network. While initially built on Polygon, it has since launched its own Layer 2 network called the Lens Network in February 2024. Lens is currently the main competitor to Farcaster. Lens stores profile ownership and references on-chain, while content is stored on IPFS/Arweave, enabling composability with DeFi and NFTs.

• Identity: Profile ownership is tied to NFTs on the Polygon blockchain.
• Storage: Content is on-chain and integrates with IPFS/Arweave (like NFTs).
• Cost: Users must pay gas fees for some operations but reading and posting messages is mostly free.

Example Message in Lens (JSON Format)

json Copy

"profileId": "@ottok", "contentURI": "ar://QmExampleHash", "collectModule": "0x23b9467334bEb345aAa6fd1545538F3d54436e96", "referenceModule": "0x0000000000000000000000000000000000000000", "timestamp": 1709558400

 
 "profileId": "@ottok",
 "contentURI": "ar://QmExampleHash",
 "collectModule": "0x23b9467334bEb345aAa6fd1545538F3d54436e96",
 "referenceModule": "0x0000000000000000000000000000000000000000",
 "timestamp": 1709558400
 

Popularity: Probably not as social media site, but maybe as protocol? The social media side of Lens is mainly the Hey.xyz website, which seems to have fewer users than Warpcast, and is even further away from reaching critical mass for network effects. The Lens protocol however has a lot of advanced features and it may gain adoption as the building block for many Web3 apps.

5. Primal.net (Nostr Network) Nostr (Notes and Other Stuff Transmitted by Relays) was conceptualized in 2020 by an anonymous developer known as fiatjaf. One of the primary design tenets was to be a censorship-resistant protocol and it is popular among Bitcoin enthusiasts, with Jack Dorsey being one of the public supporters. Unlike the Farcaster and Lens protocols, Nostr is not blockchain-based but just a network of relay servers for message distribution. If does however use public key cryptography for identities, similar to how wallets work in crypto.

• Identity: Public-private key pairs define identity (with prefix npub...).
• Storage: Content is federated among multiple servers, which in Nostr vocabulary are called relays.
• Cost: No gas fees, but relies on relay operators willing to run the servers.

Example Message in Nostr (JSON Format)

json Copy

"id": "note1xyz...", "pubkey": "npub1...", "kind": 1, "content": "Hello from Nostr!", "created_at": 1709558400, "tags": [], "sig": "sig1..."

 
 "id": "note1xyz...",
 "pubkey": "npub1...",
 "kind": 1,
 "content": "Hello from Nostr!",
 "created_at": 1709558400,
 "tags": [],
 "sig": "sig1..."
 

Popularity: If Jack Dorsey and Bitcoiners promote it enough? Primal.net as a web app is pretty solid, but it does not stand out much. While Jack Dorsey has shown support by donating $1.5 million to the protocol development in December 2021, its success likely depends on broader adoption by the Bitcoin community.

Will any of these replace X/Twitter? As usage patterns vary, the statistics are not fully comparable, but this overview of the situation in March 2025 gives a decent overview.

Platform	Total Accounts	Active Users	Growth Trend
Mastodon	~10 million	~1 million	Steady
Bluesky	~33 million	~1 million	Steady
Nostr	~41 million	~20 thousand	Steady
Farcaster	~850 thousand	~50 thousand	Flat
Lens	~140 thousand	~20 thousand	Flat

Mastodon and Bluesky have already reached millions of users, while Lens and Farcaster are growing within crypto communities. It is however clear that none of these are anywhere close to how popular X/Twitter is. In particular, Mastodon had a huge influx of users in the fall of 2022 when Twitter was acquired, but to challenge the incumbents the growth would need to significantly accelerate. We can all accelerate this development by embracing decentralized social media now alongside existing dominant platforms. Who knows, given the right circumstances maybe X.com leadership decides to change the operating model and start federating contents to break out from a walled garden model. The likelyhood of such development would increase if decentralized networks get popular, and the encumbents feel they need to participate to not lose out.

Past and future The idea of decentralized social media is not new. One early pioneer identi.ca launched in 2008, only two years after Twitter, using the OStatus protocol to promote decentralization. A few years later it evolved into pump.io with the ActivityPump protocol, and also forked into GNU Social that continued with OStatus. I remember when these happened, and that in 2010 also Diaspora launched with fairly large publicity. Surprisingly both of these still operate (I can still post both on identi.ca and diasp.org), but the activity fizzled out years ago. The protocol however survived partially and evolved into ActivityPub, which is now the backbone of the Fediverse. The evolution of decentralized social media over the next decade will likely parallel developments in democracy, freedom of speech and public discourse. While the early 2010s emphasized maximum independence and freedom, the late 2010s saw growing support for content moderation to combat misinformation. The AI era introduces new challenges, potentially requiring proof-of-humanity verification for content authenticity. Key factors that will determine success:

• User experience and ease of onboarding
• Network effects and critical mass of users
• Integration with existing web3 infrastructure
• Balance between decentralization and usability
• Sustainable economic models for infrastructure

This is clearly an area of development worth monitoring closely, as the next few years may determine which protocol becomes the de facto standard for decentralized social communication.

Tired of waiting for apt to finish installing packages? Wish there were a way to make your installations blazingly fast without caring about minor things like, oh, data integrity? Well, today is your lucky day!

What Is apt-eatmydata? If you ve ever used libeatmydata, you know it s a nifty little hack that disables fsync() and friends, making package installations way faster by skipping unnecessary disk writes. Normally, you d have to remember to wrap apt commands manually, like this:

eatmydata apt install texlive-full

But who has time for that? apt-eatmydata takes care of this automagically by integrating eatmydata seamlessly into apt itself! That means every package install is now turbocharged no extra typing required.

How to Get It

Debian If you re on Debian unstable/testing (or possibly soon in stable-backports), you can install it directly with:

sudo apt install apt-eatmydata

Ubuntu Ubuntu users already enjoy faster package installation thanks to zstd-compressed packages and to switch to even higher gear I ve backported apt-eatmydata to all supported Ubuntu releases. Just add this PPA and install:

sudo add-apt-repository ppa:firebuild/apt-eatmydata
sudo apt install apt-eatmydata

And boom! Your apt install times are getting serious upgrade. Let s run some tests

# pre-download package to measure only the installation
$ sudo apt install -d linux-headers-6.8.0-53-lowlatency
...
# installation time is 9.35s without apt-eatmydata:
$ sudo time apt install linux-headers-6.8.0-53-lowlatency
...
2.30user 2.12system 0:09.35elapsed 47%CPU (0avgtext+0avgdata 174680maxresident)k
32inputs+1495216outputs (0major+196945minor)pagefaults 0swaps
$ sudo apt install apt-eatmydata
...
$ sudo apt purge linux-headers-6.8.0-53-lowlatency
# installation time is 3.17s with apt-eatmydata: 
$ sudo time eatmydata apt install linux-headers-6.8.0-53-lowlatency
2.30user 0.88system 0:03.17elapsed 100%CPU (0avgtext+0avgdata 174692maxresident)k
0inputs+205664outputs (0major+198099minor)pagefaults 0swaps

apt-eatmydata just made installing Linux headers 3x faster!

But Wait, There s More! If you re automating CI builds, there s even a GitHub Action to make your workflows faster essentially doing what apt-eatmydata does, just setting it up in less than a second! Check it out here:
GitHub Marketplace: apt-eatmydata

Should You Use It? Warning: apt-eatmydata is not for all production environments. If your system crashes mid-install, you might end up with a broken package database. But for throwaway VMs, containers, and CI pipelines? It s an absolute game-changer. I use it on my laptop, too. So go forth and install recklessly fast! If you run into any issues, feel free to file a bug or drop a comment. Happy hacking! (To accelerate your CI pipeline or local builds, check out Firebuild, that speeds up the builds, too!)

POTA, Antennas and why do my toys not work? Having had my interest piqued by Ian at mastodon.radio, I looked online and spotted a couple of parks within stumbling distance of my house, that s good news! It looks like the list has been refactored and expanded since I last looked at it, so there are now more entities to activate and explore. My concerns about antennas noted last week rumbled on. There was a second strand to this concern too, my end fed 64:1 (or 49:1?!) transformer from MM0OPX sits in my mind as not having worked very well in Spain last year, and I want to get to the bottom of why. As with most things in my life, it s probably a me problem. I came up with a cunning plan - firstly, buy a new mast to replace the one I broke a few weeks back on Cat Law. Secondly, buy a couple of new connectors and some heatshrink to reterminate my cable that I m sure is broken. Spending more money on a problem never hurt anyone, right? Come Wednesday, the new toys arrived and I figured combining everything into one convenient night time walk and radio was a good plan. So I walk out to the nearest park with my LoRa APRS doofer going and see what happens: After circling a bit to find somewhere suitable (there appear to be construction works in the park!) I set up my gear in 2C with frost on the ground, called CQ, spotted and got nothing on either the end fed half wave or the cheap vertical. As it was too late for 20m, I tried 40 and a bit of 80 using the inbuilt tuner, but wasn t heard by stations I called or when calling independently. I packed everything up and lora-doofered my way home, mildly deflated.

Try it at home It still didn t sit with me that the end fed wasn t working, so come Friday night I set it up in the back garden/woods behind the house to try and diagnose why it wasn t working. Up it went, I worked some Irish stations pretty effortlessly, and down everything came. No complaints - the only things I did differently was have the feedpoint a little higher and check my power, limiting it to 10W. The G90 can do 20W, I wonder if running at that was saturating the core in the 64:1. At some point in the evening I stepped in some dog s shit too, and spent some time cleaning my boots outside to avoid further tramping the smell through the house. Win some, lose some.

Take it to the Hills On Friday, some of the other GM-ES Sota-ists had been out for an activity day. On account of me being busy in work, I couldn t go outside to play, but I figured a weekend of activity was on the books.

Saturday - A day above the clouds On Saturday I took myself up Tap O Noth, a favourite of mine for some reason, and Lord Arthur s Hill. Before I hit the hills, I took myself to the hackerspace and printed myself a K6ARK Winder and a guy ring for the mast, cut string, tied it together and wound the string on to the winder. I also took time to buzz out my wonky coax and it showed great continuity. Hmm, that can be continued later. I didn t quite get to crimping the radial network of the Aliexpress whip with a 12mm stud crimp, that can also be put on the TODO list.

Tap O Noth Once finally out, the weather was a bit cloudy with passing snow showers, but in between the showers I was above the clouds and the air was clear: After a mild struggle on 2m, I set up the end fed the first hill and got to work from the old hill fort: The end fed worked flawlessly. Exactly as promised, switching between 7MHz, 14MHz, 21MHz and 28MHz without a tuner was perfect, I chased hills on all the bands, and had a great time. Apart from 40m, where there was absolutely no space due to a contest. That wasn t such a fun time! My fingers were bitterly cold, so on went the big gloves for the descent and I felt like I was warm by the time I made it back to the car. It worked so well, in fact, I took the 1/4 wave cheap vertical out my bag and decided to brave it on the next activation.

Lord Arthur s Hill GM5ALX has posted a .gpx to sotlas which is shorter than the other ascent, but much sharper - I figured this would be a fun new way to try up the hill! It takes you right through the heart of the Littlewood Park estate, and I felt a bit uncomfortable walking straight past the estate cottages, especially when there were vehicles moving and active work happening. Presumably this is where Lord Arthur lived, at the foot of his hill. I cut through the woods to the west of the cottages, disturbing some deer and many, many pheasants, but I met the path fairly quickly. From there it was a 2km walk, 300m vertical ascent. Short and sharp! At the top, I was treated to a view of the hill I had activated only an hour or so before, which is a view that always makes me smile: To get some height for the feedpoint, I wrapped the coax around my winder a couple of turns and trapped it with the elastic while draping the coax over the trig. This bought me some more height and I felt clever because of it. Maybe a pole would be easier? From here, I worked inter-G on 40m and had a wee pile up, eventually working 15 or so European stations on 20m. Pleased with that! I had been considering a third hill, but home was the call in the failing light. Back to the car I walked to find my key didn t have any battery, so out came the Audi App and I used the Internet of Things to unlock my car. The modern world is bizarre.

Sunday - Cloudy Head // Head in the Clouds Sunday started off migraney, so I stayed within the confines of my house until I felt safe driving! After some back and forth in my cloudy head, I opted for the easier option of Ladylea Hill as I wasn t feeling up for major physical exertion. It was a long drive, after which I felt more wonky, but I hit the path eventually - I run to Hibby Standard Time, a few hours to a few days behind the rest of GM/ES. I was ready to bail if my head didn t improve, but it turns out, fresh cold air, silence and bloodflow helped. Ladylea Hill was incredibly quiet, a feature I really appreciated. It feels incredibly remote, with a long winding drive down Glenbuchat, which still has ice on the surface of the lochs and standing water. A brooding summit crowned with grey cloud in fantastic scenery that only revealed itself upon the clouds blowing through: I set up at the cairn and picked up 30 contacts overall, split between 40m and 20m, with some inter-g on 40 and a couple of continental surprises. 20 had longer skip today, so I saw Spain, Finland, Slovenia, Poland. On teardown, I managed to snap the top segment of my brand new mast with my cold, clumsy fingers, but thankfully sotabeams stock replacements. More money at the problem, again. Back to the car, no app needed, and homeward bound as the light faded. At the end of the weekend, I find myself finally over 100 activator points and over 400 chaser points. Somehow I ve collected more points this year already than last year, the winter bonuses really do stack up!

Addendum - OSMAnd & Open Street Map I ve been using OSMAnd on my iPhone quite extensively recently, I think offline mapping is super important if you re going out to get mildly lost in the hills. On more than one occasion, I have confidently set off in the wrong direction in the mist, and maps have saved my bacon! As you can download .gpx files, it s great to have them on the device and available for guidance in case you get lost, coupled with an offline map. Plus, as I drive around I love to have the dark red of a hill I ve walked appear on the map in my car dash or in my hand: This weekend I discovered it s possible to have height maps for nice 3d maps and contours marked on the map - you just need to download some additions for the maps. This is a really nice feature, it makes maps more pretty and more useful when you re in the middle of nowhere. Open Street Map also has designators for SOTA summits here and similar for POTA here GM5ALX has set to adding the summits around Scotland here. While the benefits aren t immediately obvious, it allows developers of mapping applications access to more data at no extra cost, really. It helps add depth to an already rich set of information, and allows us as radio amateurs to do more interesting things with maps and not be shackled to Apple/Google. Because it s open data, we can also fix things we find wrong as users. I like to fix road surfaces after I ve been cycling as that will feed forward to route planning through Komoot and data on my wahoo too, which can be modified with osm maps. In the future, it s possible to have an OSMAnd plugin highlighting local SOTA summits or mimicking features of sotl.as but offline. It s cool to be able to put open technologies to use like this in the field and really is the convergence point of all my favourite things!

1. reproduce.debian.net
2. Two new academic papers
3. Distribution work
4. On our mailing list
5. Upstream patches
6. diffoscope
7. Website updates
8. Reproducibility testing framework

reproduce.debian.net The last few months saw the introduction of reproduce.debian.net. Announced at the recent Debian MiniDebConf in Toulouse, reproduce.debian.net is an instance of rebuilderd operated by the Reproducible Builds project. Powering that is rebuilderd, our server designed monitor the official package repositories of Linux distributions and attempt to reproduce the observed results there. This month, however, we are pleased to announce that in addition to the existing amd64.reproduce.debian.net and i386.reproduce.debian.net architecture-specific pages, we now build for a three more architectures (for a total of five) arm64 armhf and riscv64.

Two new academic papers Giacomo Benedetti, Oreofe Solarin, Courtney Miller, Greg Tystahl, William Enck, Christian K stner, Alexandros Kapravelos, Alessio Merlo and Luca Verderame published an interesting article recently. Titled An Empirical Study on Reproducible Packaging in Open-Source Ecosystem, the abstract outlines its optimistic findings:

[We] identified that with relatively straightforward infrastructure configuration and patching of build tools, we can achieve very high rates of reproducible builds in all studied ecosystems. We conclude that if the ecosystems adopt our suggestions, the build process of published packages can be independently confirmed for nearly all packages without individual developer actions, and doing so will prevent significant future software supply chain attacks.

The entire PDF is available online to view.
In addition, Julien Malka, Stefano Zacchiroli and Th o Zimmermann of T l com Paris in-house research laboratory, the Information Processing and Communications Laboratory (LTCI) published an article asking the question: Does Functional Package Management Enable Reproducible Builds at Scale?. Answering strongly in the affirmative, the article s abstract reads as follows:

In this work, we perform the first large-scale study of bitwise reproducibility, in the context of the Nix functional package manager, rebuilding 709,816 packages from historical snapshots of the nixpkgs repository[. We] obtain very high bitwise reproducibility rates, between 69 and 91% with an upward trend, and even higher rebuildability rates, over 99%. We investigate unreproducibility causes, showing that about 15% of failures are due to embedded build dates. We release a novel dataset with all build statuses, logs, as well as full diffoscopes: recursive diffs of where unreproducible build artifacts differ.

As above, the entire PDF of the article is available to view online.

Distribution work There as been the usual work in various distributions this month, such as:

• Arch Linux developer kpcyrd has provided a status report for January 2025 related to Arch s progress towards full reproducibility. kpcyrd notes in particular progress towards to making a minimal reproducible bootable system that is, an Arch installation containing only reproducible packages.

• 10+ reviews of Debian packages were added, 11 were updated and 10 were removed this month adding to our knowledge about identified issues. A number of issue types were updated also.
• The FreeBSD Foundation announced that a planned project to deliver zero-trust builds has begun in January 2025 . Supported by the Sovereign Tech Agency, this project is centered on the various build processes, and that the primary goal of this work is to enable the entire release process to run without requiring root access, and that build artifacts build reproducibly that is, that a third party can build bit-for-bit identical artifacts. The full announcement can be found online, which includes an estimated schedule and other details.

• Finally, for openSUSE, Bernhard M. Wiedemann published another report for that distribution.

On our mailing list On our mailing list this month:

• Following-up to a substantial amount of previous work pertaining the Sphinx documentation generator, James Addison asked a question pertaining to the relationship between SOURCE_DATE_EPOCH environment variable and testing that generated a number of replies.
• Adithya Balakumar of Toshiba asked a question about whether it is possible to make ext4 filesystem images reproducible. Adithya s issue is that even the smallest amount of post-processing of the filesystem results in the modification of the Last mount and Last write timestamps.
• James Addison also investigated an interesting issue surrounding our disorderfs filesystem. In particular:

  FUSE (Filesystem in USErspace) filesystems such as disorderfs do not delete files from the underlying filesystem when they are deleted from the overlay. This can cause seemingly straightforward tests for example, cases that expect directory contents to be empty after deletion is requested for all files listed within them to fail.

Upstream patches The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where appropriate. This month, we wrote a large number of such patches, including:

• Bernhard M. Wiedemann:
  • Komikku (nocheck)
  • abseil-cpp (race)
  • dunst (date)
  • eclipse-egit (jar-mtime minor)
  • exaile (race)
  • gawk (bug)
  • gimp3 (png date)
  • intel (ASLR)
  • ioquake3 (debugsource contains date and time)
  • joker (sort)
  • libchardet
  • llama.cpp (random)
  • llama.cpp (-march=native-related issue)
  • nethack (race)
  • netrek-client-cow (date)
  • nvidia-modprobe (date)
  • nvidia-persistenced (date)
  • obs-build (toolchain bug, mis-parses changelog)
  • perl-libconfigfile (race)
  • pgvector (CPU)
  • python-Django4 (FTBFS-2038)
  • python-python-datamatrix (FTBFS)
  • qore-ssh2-module (GIGO-bug)
  • rpm (UID in cpio header from rpmbuild)
  • zig (CPU-related issue)
• Chris Lamb:
  • #1092251 filed against kmetronome.
  • #1092917 filed against rust-xh.
  • #1093198 filed against parser.
  • #1093199 filed against parser.
  • #1093201 filed against rsync.
  • #1094611 filed against wasistlos.
• Egbert Eich:
  • apptainer (randomness)
  • spack (core-count and date)
• Valentin Lefebvre:
  • uki-tool (toolchain)
• Marvin Friedrich:
  • cargo-packaging/rusty_v8 (upstream toolchain bugfix)
• James Addison:
  • #1092870 filed against binutils.
• Pol Dellaiera:
  • PHP Ecosystem: composer/composer#12090 which was then gracefully fixed by Jordi Boggiano at composer/composer#12263.

diffoscope diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues. This month, Chris Lamb made the following changes, including preparing and uploading versions 285, 286 and 287 to Debian:

• Security fixes:
  • Validate the --css command-line argument to prevent a potential Cross-site scripting (XSS) attack. Thanks to Daniel Schmidt from SRLabs for the report. [ ]
  • Prevent XML entity expansion attacks. Thanks to Florian Wilkens from SRLabs for the report.. [ ][ ]
  • Print a warning if we have disabled XML comparisons due to a potentially vulnerable version of pyexpat. [ ]
• Bug fixes:
  • Correctly identify changes to only the line-endings of files; don t mark them as Ordering differences only. [ ]
  • When passing files on the command line, don t call specialize( ) before we ve checked that the files are identical or not. [ ]
  • Do not exit with a traceback if paths are inaccessible, either directly, via symbolic links or within a directory. [ ]
  • Don t cause a traceback if cbfstool extraction failed.. [ ]
  • Use the surrogateescape mechanism to avoid a UnicodeDecodeError and crash when any decoding zipinfo output that is not UTF-8 compliant. [ ]
• Testsuite improvements:
  • Don t mangle newlines when opening test fixtures; we want them untouched. [ ]
  • Move to assert_diff in test_text.py. [ ]
• Misc improvements:
  • Drop unused subprocess imports. [ ][ ]
  • Drop an unused function in iso9600.py. [ ]
  • Inline a call and check of Config().force_details; no need for an additional variable in this particular method. [ ]
  • Remove an unnecessary return value from the Difference.check_for_ordering_differences method. [ ]
  • Remove unused logging facility from a few comparators. [ ]
  • Update copyright years. [ ][ ]

In addition, fridtjof added support for the ASAR .tar-like archive format. [ ][ ][ ][ ] and lastly, Vagrant Cascadian updated diffoscope in GNU Guix to version 285 [ ][ ] and 286 [ ][ ].
strip-nondeterminism is our sister tool to remove specific non-deterministic results from a completed build. This month version 1.14.1-1 was uploaded to Debian unstable by Chris Lamb, making the following the changes:

• Clarify the --verbose and non --verbose output of bin/strip-nondeterminism so we don t imply we are normalizing files that we are not. [ ]
• Bump Standards-Version to 4.7.0. [ ]

Website updates There were a large number of improvements made to our website this month, including:

• Arnout Engelen:
  • Update the link to NixOS reproducibility-related issue template on the NixOS-specific contribute page [ ] and remove an outdated link. [ ]
• Holger Levsen:
  • Check, deduplicate, update and generally cleanup a number of presentations linked on our Talks & Resources page. [ ][ ][ ][ ]
• James Addison:
  • Add some file permissions hints and guidance on the Archive metadata page. [ ]
• Michael R. Crusoe:
  • Add an R example to the SOURCE_DATE_EPOCH documentation. [ ]
  • Update the website s README to make the setup command copy & paste friendly. [ ]

Reproducibility testing framework The Reproducible Builds project operates a comprehensive testing framework running primarily at tests.reproducible-builds.org in order to check packages and other artifacts for reproducibility. In January, a number of changes were made by Holger Levsen, including:

• reproduce.debian.net-related:
  • Add support for rebuilding the armhf architecture. [ ][ ]
  • Add support for rebuilding the arm64 architecture. [ ][ ][ ][ ]
  • Add support for rebuilding the riscv64 architecture. [ ][ ]
  • Move the i386 builder to the osuosl5 node. [ ][ ][ ][ ]
  • Don t run our rebuilders on a public port. [ ][ ]
  • Add database backups on all builders and add links. [ ][ ]
  • Rework and dramatically improve the statistics collection and generation. [ ][ ][ ][ ][ ][ ]
  • Add contact info to the main page [ ], thumbnails [ ] as well as the new, missing architectures. [ ]
  • Move the amd64 worker to the osuosl4 and node. [ ]
  • Run the underlying debrebuild script under nice. [ ]
  • Try to use TMPDIR when calling debrebuild. [ ][ ]
• buildinfos.debian.net-related:
  • Stop creating buildinfo-pool_$ suite _$ arch .list files. [ ]
  • Temporarily disable automatic updates of pool links. [ ]
• FreeBSD-related:
  • Fix the sudoers to actually permit builds. [ ]
  • Disable debug output for FreeBSD rebuilding jobs. [ ]
  • Upgrade to FreeBSD 14.2 [ ] and document that bmake was installed on the underlying FreeBSD virtual machine image [ ].
• Misc:
  • Update the real year to 2025. [ ]
  • Don t try to install a Debian bookworm kernel from backports on the infom08 node which is running Debian trixie. [ ]
  • Don t warn about system updates for systems running Debian testing. [ ]
  • Fix a typo in the ZOMBIES definition. [ ][ ]

In addition:

• Ed Maste modified the FreeBSD build system to the clean the object directory before commencing a build. [ ]
• Gioele Barabucci updated the rebuilder stats to first add a category for network errors [ ] as well as to categorise failures without a diffoscope log [ ].
• Jessica Clarke also made some FreeBSD-related changes, including:
  • Ensuring we clean up the object directory for second build as well. [ ][ ]
  • Updating the sudoers for the relevant rm -rf command. [ ]
  • Update the cleanup_tmpdirs method to to match other removals. [ ]
• Jochen Sprickerhof:
  • Fix logic for old files saved on buildinfos.debian.net. [ ]
  • Rework and simplify the generation of statistics linked from reproduce.debian.net. [ ][ ][ ][ ]
• Roland Clobus:
  • Update the reproducible_debstrap job to call Debian s debootstrap with the full path [ ] and to use eatmydata as well [ ][ ].
  • Make some changes to deduce the CPU load in the debian_live_build job. [ ]

Lastly, both Holger Levsen [ ] and Vagrant Cascadian [ ] performed some node maintenance.
If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

• IRC: #reproducible-builds on irc.oftc.net.
• Mastodon: @reproducible_builds@fosstodon.org
• Mailing list: rb-general@lists.reproducible-builds.org
• Twitter: @ReproBuilds

This post is a review for Computing Reviews for The science of detecting LLM-generated text , a article published in Communications of the ACM

• [1] https://etbe.coker.com.au/2024/07/23/more-5120 2160-monitor/
• [2] https://daniel.lawrence.lu/blog/y2023m12d15/

The new Firebuild release contains plenty of small fixes and a few notable improvements.

Experimental macOS support The most frequently asked question from people getting to know Firebuild was if it worked on their Mac and the answer sadly used to be that well, it did, but only in a Linux VM. This was far from what they were looking for. Linux and macOS have common UNIX roots, but porting Firebuild to macOS included bigger challenges, like ensuring that dyld(1), macOS s dynamic loader initializes the preloaded interceptor library early enough to catch all interesting calls, and avoid using anything that uses malloc() or thread local variables which are not yet set up then. Preloading libraries on Linux is really easy, running LD_PRELOAD=my_lib.so ls just works if the library exports the symbols to be interposed, while macOS employs multiple lines of defense to prevent applications from using unknown libraries. Firebuild s guide for making DYLD_INSERT_LIBRARIES honored on Macs can be helpful with other projects as well that rely on injecting libraries. Since GitHub s Arm64 macOS runners don t allow intercepting binaries with arm64e ABI yet, Firebuild s Apple Silicon tests are run at Bitrise, who are proud to be first to provide the latest Xcode stacks and were also quick to make the needed changes to their infrastructure to support Firebuild (thanks! ). Firebuild on macOS can already accelerate simple projects and rebuild itself with Xcode. Since Xcode introduces a lot of nondeterminism to the build, Firebuild can t shine in acceleration with Xcode yet, but can provide nice reports to show which part of the build is the most time consuming and how each sub-command is called. If you would like to try Firebuild on macOS please compile it from the GitHub repository for now. Precompiled binaries will be distributed on the Mac App Store and via CI providers. Contact us to get notified when those channels become available.

Dealing with the Epochalypse Glibc s API provides many functions with time parameters and some of those functions are intercepted by Firebuild. Time parameters used to be passed as 32-bit values on 32-bit systems, preventing them to accurately represent timestamps after year 2038, which is known as the Y2038 problem or the Epochalypse. To deal with the problem glibc 2.34 started providing new function symbol variants with 64-bit time parameters, e.g clock_gettime64() in addition to clock_gettime(). The new 64-bit variants are used when compiling consumers of the API with _TIME_BITS=64 defined. Processes intercepted by Firebuild may have been compiled with or without _TIME_BITS=64, thus libfirebuild now provides both variants on affected systems running glibc >= 34 to work safely with binaries using 64-bit and 32-bit time representation. Many Linux distributions already stopped supporting 32-bit architectures, but Debian and Ubuntu still supports armhf, for example, where the Y2038 problem still applies. Both Debian and Ubuntu performed a transition rebuilding every library (and their reverse dependencies) with -D_FILE_OFFSET_BITS=64 set where the libraries exported symbols that changed when switching to 64-bit time representation (thanks to Steve Langasek for driving this!) . Thanks to the transition most programs are ready for 2038, but interposer libraries are trickier to fix and if you maintain one it might be a good idea to check if it works well both 32-bit and 64-bit libraries. Faketime, for example is not fixed yet, see #1064555.

Select passed through environment variables with regular expressions Firebuild filters out most of the environment variables set when starting a build to make the build more reproducible and achieve higher cache hit rate. Extra environment variables to pass through can be specified on the command line one by one, but with many similarly named variables this may become hard to maintain. With regular expressions this just became easier:

firebuild -o 'env_vars.pass_through += "MY_VARS_.*"' my_build_command

If you are not interested in acceleration just would like to explore what the build does by generating a report you can simply pass all variables:

firebuild -r -o 'env_vars.pass_through += ".*"' my_build_command

Other highlights from the 0.8.3 release

• Fixed and nicer report in Chrome and other WebKit based browsers
• Support GLibc 2.39 by intercepting pidfd_spawn() and pidfd_spawnp()
• Even faster Rust build acceleration

For all the changes please check out the release page on GitHub! (This post is also published on The Firebuild blog.)

• Joachim Bauch (fancycode)
• Alexander Kj ll (capitol)
• Jan Moj (janmojzis)
• Xiao Sheng Wen (atzlinux)

• Alberto Bertogli
• Alexis Murzeau
• David Heilderberg
• Xiyue Deng
• Kathara Sasikumar
• Philippe Swartvagher

The coffee shop Ibtehal and me used to visit during the midnight

Grating at a chemist shop in Mombasa, Kenya

A visit to Nairobi s Historic Cricket Ground On this trip, I got a unique souvenir that can t be purchased from the market a cricket jersey worn in an ODI match by a player. The story goes as follows: I was roaming around the market with my friend Benson from Nairobi to buy a Kenyan cricket jersey for myself, but we couldn t find any. So, Benson had the idea of visiting the Nairobi Gymkhana Club, which used to be Kenya s main cricket ground. It has hosted some historic matches, including the 2003 World Cup match in which Kenya beat the mighty Sri Lankans and the record for the fastest ODI century by Shahid Afridi in just 37 balls in 1996. Although entry to the club was exclusively for members, I was warmly welcomed by the staff. Upon reaching the cricket ground, I met some Indian players who played in Kenyan leagues, as well as Lucas Oluoch and Dominic Wesonga, who have represented Kenya in ODIs. When I expressed interest in getting a jersey, Dominic agreed to send me pictures of his jersey. I liked his jersey and collected it from him. I gave him 2000 shillings, an amount suggested by those Indian players.

Me with players at the Nairobi Gymkhana Club

Cricket pitch at the Nairobi Gymkhana Club

A view of the cricket ground inside the Nairobi Gymkhana Club

Scoreboard at the Nairobi Gymkhana cricket ground

Giraffe Center in Nairobi Kenya is known for its safaris and has no shortage of national parks. In fact, Nairobi is the only capital in the world with a national park. I decided not to visit one, as most of them were expensive and offered multi-day tours, and I didn t want to spend that much time in the wildlife. Instead, I went to the Giraffe Center in Nairobi with Pragya and Rabina. The ticket cost 1500 Kenyan shillings (1000 Indian rupees). In Kenya, matatus - shared vans, usually decorated with portraits of famous people and play rap songs - are the most popular means of public transport. Reaching the Giraffe Center from our hotel required taking five matatus, which cost a total of 150 shillings, and a 2 km walk. The journey back was 90 shillings, suggesting that we didn t find the most efficient route to get there. At the Giraffe Center, we fed giraffes and took photos.

A matatu with a Notorious BIG portrait.

Inside the Giraffe Center

Train ride from Nairobi to Mombasa I took a train from Nairobi to Mombasa. The train is known as the SGR Train, where SGR refers to Standard Gauge Railway. The journey was around 500 km. M-Pesa was the only way to make payment for pre-booking the train ticket, and I didn t have an M-Pesa account. Pragya s friend Mary helped facilitate the payment. I booked a second-class ticket, which cost 1500 shillings (1000 Indian rupees). The train was scheduled to depart from Nairobi at 08:00 hours in the morning and arrive in Mombasa at 14:00 hours. The security check at the station required scanning our bags and having them sniffed by sniffer dogs. I also fell victim to a scam by a security official who offered to help me get my ticket printed, only to later ask me to get him some coffee, which I politely declined. Before boarding the train, I was treated to some stunning views at the Nairobi Terminus station. It was a seating train, but I wished it were a sleeper train, as I was sleep-deprived. The train was neat and clean, with good toilets. The train reached Mombasa on time at around 14:00 hours.

SGR train at Nairobi Terminus.

Interior of the SGR train

Arrival in Mombasa

Mombasa Terminus station.

Mombasa was a bit hotter than Nairobi, with temperatures reaching around 30 degrees Celsius. However, that s not too hot for me, as I am used to higher temperatures in India. I had booked a hostel in the Old Town and was searching for a hitchhike from the Mombasa Terminus station. After trying for more than half an hour, I took a matatu that dropped me 3 km from my hostel for 200 shillings (140 Indian rupees). I tried to hitchhike again but couldn t find a ride. I think I know why I couldn t get a ride in both the cases. In the first case, the Mombasa Terminus was in an isolated place, so most of the vehicles were taxis or matatus while any noncommercial cars were there to pick up friends and family. If the station were in the middle of the city, there would be many more car/truck drivers passing by, thus increasing my possibilities of getting a ride. In the second case, my hostel was at the end of the city, and nobody was going towards that side. In fact, many drivers told me they would love to give me a ride, but they were going in some other direction. Finally, I took a tuktuk for 70 shillings to reach my hostel, Tulia Backpackers. It was 11 USD (1400 shillings) for one night. The balcony gave a nice view of the Indian Ocean. The rooms had fans, but there was no air conditioning. Each bed also had mosquito nets. The place was walking distance of the famous Fort Jesus. Mombasa has had more Islamic influence compared to Nairobi and also has many Hindu temples.

The balcony at Tulia Backpackers Hostel had a nice view of the ocean.

A room inside the hostel with fans and mosquito nets on the beds

Visiting White Sandy Beaches and Getting a Hitchhike Visiting Nyali beach marked my first time ever at a white sand beach. It was like 10 km from the hostel. The next day, I visited Diani Beach, which was 30 km from the hostel. Going to Diani Beach required crossing a river, for which there s a free ferry service every few minutes, followed by taking a matatu to Ukunda and then a tuk-tuk. The journey gave me a glimpse of the beautiful countryside of Kenya.

Nyali beach is a white sand beach

This is the ferry service for crossing the river.

During my return from Diani Beach to the hostel, I was successful in hitchhiking. However, it was only a 4 km ride and not sufficient to reach Ukunda, so I tried to get another ride. When a truck stopped for me, I asked for a ride to Ukunda. Later, I learned that they were going in the same direction as me, so I got off within walking distance from my hostel. The ride was around 30 km. I also learned the difference between a truck ride and a matatu or car ride. For instance, matatus and cars are much faster and cooler due to air conditioning, while trucks tend to be warmer because they lack it. Further, the truck was stopped at many checkpoints by the police for inspections as it carried goods, which is not the case with matatus. Anyways, it was a nice experience, and I am grateful for the ride. I had a nice conversation with the truck drivers about Indian movies and my experiences in Kenya.

Diani beach is a popular beach in Kenya. It is a white sand beach.

Selfie with truck drivers who gave me the free ride

Back to Nairobi I took the SGR train from Mombasa back to Nairobi. This time I took the night train, which departs at 22:00 hours, reaching Nairobi at around 04:00 in the morning. I could not sleep comfortably since the train only had seater seats. I had booked the Zarita Hotel in Nairobi and had already confirmed if they allowed early morning check-in. Usually, hotels have a fixed checkout time, say 11:00 in the morning, and you are not allowed to stay beyond that regardless of the time you checked in. But this hotel checked me in for 24 hours. Here, I paid in US dollars, and the cost was 12 USD.

Almost Got Stuck in Kenya Two days before my scheduled flight from Nairobi back to India, I heard the news that the airports in Kenya were closed due to the strikes. Rabina and Pragya had their flight back to Nepal canceled that day, which left them stuck in Nairobi for two additional days. I called Sahil in India and found out during the conversation that the strike was called off in the evening. It was a big relief for me, and I was fortunate to be able to fly back to India without any changes to my plans.

Newspapers at a stand in Kenya covering news on the airport closure

Experience with locals I had no problems communicating with Kenyans, as everyone I met knew English to an extent that could easily surpass that of big cities in India. Additionally, I learned a few words from Kenya s most popular local language, Swahili, such as Asante, meaning thank you, Jambo for hello, and Karibu for welcome. Knowing a few words in the local language went a long way. I am not sure what s up with haggling in Kenya. It wasn t easy to bring the price of souvenirs down. I bought a fridge magnet for 200 shillings, which was the quoted price. On the other hand, it was much easier to bargain with taxis/tuktuks/motorbikes. I stayed at three hotels/hostels in Kenya. None of them had air conditioners. Two of the places were in Nairobi, and they didn t even have fans in the rooms, while the one in Mombasa had only fans. All of them had good Wi-Fi, except Tulia where the internet overall was a bit shaky. My experience with the hotel staff was great. For instance, we requested that the Nairobi Transit Hotel cancel the included breakfast in order to reduce the room costs, but later realized that it was not a good idea. The hotel allowed us to revert and even offered one of our missing breakfasts during dinner. The staff at Tulia Backpackers in Mombasa facilitated the ticket payment for my train from Mombasa to Nairobi. One of the staff members also gave me a lift to the place where I could catch a matatu to Nyali Beach. They even added an extra tea bag to my tea when I requested it to be stronger.

Food At the Nairobi Transit Hotel, a Spanish omelet with tea was served for breakfast. I noticed that Spanish omelette appeared on the menus of many restaurants, suggesting that it is popular in Kenya. This was my first time having this dish. The milk tea in Kenya, referred to by locals as white tea, is lighter than Indian tea (they don t put a lot of tea leaves).

Spanish Omelette served in breakfast at Nairobi Transit Hotel

I also sampled ugali with eggs. In Mombasa, I visited an Indian restaurant called New Chetna and had a buffet thali there twice.

Ugali with eggs.

Tips for Exchanging Money In Kenya, I exchanged my money at forex shops a couple of times. I received good exchange rates for bills larger than 50 USD. For instance, 1 USD on xe.com was 129 shillings, and I got 128.3 shillings per USD (a total of 12,830 shillings) for two 50 USD notes at an exchange in Nairobi, while 127 shillings, which was the highest rate at the banks. On the other hand, for smaller bills such as a one US dollar note, I would have got 125 shillings. A passport was the only document required for the exchange, and they also provided a receipt. A good piece of advice for travelers is to keep 50 USD or larger bills for exchanging into the local currency while saving the smaller US dollar bills for accommodation, as many hotels and hostels accept payment in US dollars (in addition to Kenyan shillings).

Missed Malindi and Lamu There were more places on my to-visit list in Kenya. But I simply didn t have time to cover them, as I don t like rushing through places, especially in a foreign country where there is a chance of me underestimating the amount of time it takes during transit. I would have liked to visit at least one of Kilifi, Watamu or Malindi beaches. Further, Lamu seemed like a unique place to visit as it has no cars or motorized transport; the only options for transport are boats and donkeys. That s it for now. Meet you in the next one :)