Played Shape Chess (形棋) this weekend, a great new board game from China by Richu (日出). The goal is to make mirror-symmetric shapes while stopping your opponent from doing the same. Just a grid and pieces in two colors. A great English intro to the game: blackandwhite.develz.org/games/ShapeC...

And, although it is usually credited to Dirichlet, the principle was introduced earlier in a Jesuit mathematics textbook written in Latin by Jean Leurechon. Makes me wonder if there are even earlier formulations in non-Indo-European languages. backoffice.biblio.ugent.be/download/411...

Why is this hard? I found a lovely paper from Mercier, Politzer, & Sperber contrasting cardinal with nominal framings of pigeonhole problems. People seem to find nominal framings intuitive—if you run 3 errands in 2 days, one day will have at least 2 errands. Easy! www.dan.sperber.fr/wp-content/u...

Despite its dearness to my heart, my understanding of the principle has long lived on the stunted, spatially metaphorical level of Dijkstra's unfortunate colleague, described here. So this was a bit of a harrowing read!

Working on a hobby project using a favorite math concept: the pigeonhole principle. To wit: Given n boxes holding >n objects, at least one box must hold >1 objects. I stumbled on this (charming, arrogant) reformulation from Dijkstra, in his beautiful handwriting: www.cs.utexas.edu/~EWD/ewd09xx...

Similarly: