rntz
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rntz
@rntz.net
360 followers 170 following 320 posts
Michael Arntzenius irl. Postdoc at UC Berkeley doing PL + DB + incremental computation. PL design, math, calligraphy, idle musings, &c.

rntz.net
🐘 @[email protected]
🐦 @arntzenius

Attempting to use bsky more now that people are showing up.
Posts Replies Media Videos
are enclose.horse puzzles getting easier or am I just gitting gud?
a screenshot of "past puzzles" page from enclose.horse, showing my performance. the exact scores are censored out but days 13-21 are all diamond (perfect); before that is a mix of gold and occasional diamond.
January 19, 2026 at 6:22 PM
It's well known that set intersection is associative. Unfortunately:

import Data.Set
n = 20_000_000
evens = fromList [0,2..n]
odds = fromList [1,3..n]
ends = fromList [0,n]
fast = evens `intersection` (odds `intersection` ends)
slow = (evens `intersection` odds) `intersection` ends
January 18, 2026 at 3:44 PM
repost (boosting reach)
repost (moral agreement)
repost (aspirational)
repost (compliment)
repost (mockery)
repost (cat pic)
repost (i got rickrolled)
January 17, 2026 at 6:57 PM
modal dialogs delendi sunt
January 17, 2026 at 6:28 PM
there is a direct correlation between how anxious I get about <waves hands> and how many james hoffmann videos I watch
January 17, 2026 at 5:22 PM
Sophic is to Sophomoric
as
Sapphic is to Sapphomoric,

obviously
January 15, 2026 at 8:31 PM
Reposted by rntz
andrew.heiss.phd
More evidence supporting this really neat paper doi.org/10.1111/ajps... (JSTOR version: www.jstor.org/stable/45295...)
Why Underachievers Dominate Secret Police Organizations: Evidence from Autocratic Argentina Adam Scharpf, Christian Gläßel American Journal of Political Science Volume 64, Issue 4 October 2020 Pages 791-806 Abstract Autocrats depend on a capable secret police. Anecdotal evidence, however, often characterizes agents as surprisingly mediocre in skill and intellect. To explain this puzzle, this article focuses on the career incentives underachieving individuals face in the regular security apparatus. Low-performing officials in hierarchical organizations have little chance of being promoted or filling lucrative positions. To salvage their careers, these officials are willing to undertake burdensome secret police work. Using data on all 4,287 officers who served in autocratic Argentina (1975–83), we study biographic differences between secret police agents and the entire recruitment pool. We find that low-achieving officers were stuck within the regime hierarchy, threatened with discharge, and thus more likely to join the secret police for future benefits. The study demonstrates how state bureaucracies breed mundane career concerns that produce willing enforcers and cement violent regimes. This has implications for the understanding of autocratic consolidation and democratic breakdown.
October 23, 2025 at 2:21 PM
Reposted by rntz
musaalgharbi.bsky.social
My latest for @bostonglobe.com analyzes the killing of #ReneeNicoleGood, and explains why no amount of video footage -- regardless of the angle or quality -- will put to rest the polarization over the tragedy and it's implications.

🧵
All the videos in the world won’t end the argument over Renee Good’s death
I’ve seen the videos of the fatal shooting in Minneapolis several times and from many different angles.
globeopinion.substack.com
January 10, 2026 at 6:49 PM
Some people, when confronted with a problem, think “I know, I’ll use dependent types.” Now they have several open research questions.
December 31, 2025 at 10:15 PM
Bidirectional typing can be implemented with two functions,

check: term → type → bool
synth: term → maybe type

I like to merge them,

elab: term → maybe type → maybe type

elab x None infers; elab x (Some t) checks. This makes it easy to handle eg let-binding, which can either infer or check.
December 31, 2025 at 6:02 PM
Chuck Tingle's new Booker-prize-winning historical fanfiction, Lincoln in the Birdo
December 30, 2025 at 10:39 PM
a diptych:
1. oh my god I love NYC
2. I am so tired oh my god
December 28, 2025 at 9:17 PM
IIII'm John Ronald Reuel Tolkiën
John Ronald Reuel Tolkiën-iën

(to the tune of "I'm Henry the VIII, I am", natch: www.youtube.com/watch?v=GisC...)
Herman's Hermits "I'm Henry VIII, I Am" on The Ed Sullivan Show
YouTube video by The Ed Sullivan Show
www.youtube.com
December 28, 2025 at 3:09 PM
unexpectedly stranded in NYC b/c my flight out rejected me at boarding for not having travel insurance (?!?). Anyone in NYC either/both
a) wanna meet up tomorrow (Dec 28)?
b) happy to put me up for 1-2 nights until I find a flight?
December 28, 2025 at 7:41 AM
every corner —
I have cut it —
nevertheless!
Í háve submítted
December 17, 2025 at 9:48 AM
writing about direct & smash products in pointed sets in a paper draft and desperately trying to find a smash bros joke to sneak in
December 15, 2025 at 2:25 AM
I have decided to have fun with the section titles in my paper-to-be, at least while I'm writing it.
1 Logic programming is (not) functional programming 2 Support, pointedly 3 Why not just...? 4 A finitely supported map from examples to booleans 5 The relevance of being relevant 6 Context hopping 7 Curing maybe-addiction with class 8 What does it all mean?
December 13, 2025 at 6:07 AM
Reposted by rntz
dirtside.bsky.social
This is part 4 of subpart 9 of our 15-part (I, II, III, IV, V, VI, VII, VIIIa, VIIIb, VIIIc-1, VIIIc-2, IX, IX with clusters, IX with honey nut clusters, X, XI, XII: Tokyo Drift, XIII, XIV, XV) series that lists all the other articles on this blog. If you donate I will buy the Pentagon.
December 1, 2025 at 10:04 PM
Reposted by rntz
nsaphra.bsky.social
Engagement KPIs have been responsible for infinite scroll UI traps, RecSys radicalization spirals, public shame brigades, and basically every modern ailment novel to the past decade. At some point, you have to recognize that the problem isn't any one technology, it's the metric.
kashhill.bsky.social Kashmir Hill @kashhill.bsky.social · Nov 23
The company essentially turned a dial that made ChatGPT more appealing and made people use it more, but sent some of them into delusional spirals.

OpenAI has since made the chatbot safer, but that comes with a tradeoff: less usage.
November 23, 2025 at 8:12 PM
everything good is bad. everything strong is weak. what you want you don't need; you need just what you don't want.
November 17, 2025 at 7:09 AM
Reposted by rntz
galaxykate.bsky.social
Doctor says, 'Dont worry, parser design is simple. Great programmer Kate Compton has written the parser you seek’
Conversation with Claude about tracery parsers, and it advises me to look at kate comptons parser, to which i reply “but Doctor i am kate compton”
November 16, 2025 at 2:44 PM
a geometric visualization of factorized delta queries by @jcreed.bsky.social, representing
Δ(R ∧ S ∧ T) = (ΔR ∧ S ∧ T) ∨ (R' ∧ ΔS ∧ T) ∨ (R' ∧ S' ∧ ΔT)
where R' = R ∨ ΔR etc.
November 16, 2025 at 9:24 PM
a numbered heading from a pdf document: 1 Logic Programming is (not) Functional Programming
November 16, 2025 at 1:47 AM
today I thought "hm, maybe I should reread the Count of Monte Cristo". but you know what they say: vita brevis, ars longa.
November 1, 2025 at 7:14 AM
My miniKanren 2025 paper, "Fair intersection of seekable iterators", about an efficient, compositional way to implement relational joins on sorted data structures, and how it (sorta) requires "fairness", is now on arXiv: arxiv.org/abs/2510.26016

talk slides: www.rntz.net/files/minika...
October 31, 2025 at 6:58 PM