ok here's a more concrete + human understandable proof of uncountability
---
RT @pawnofcthulhu
cute
one quote "the tile admits uncountably many tilings": is it even possible to have a set of tiles that aperiodically tile the plane without having uncountably many tilings? twitter.com/cs_kaplan/status/1
twitter.com/pawnofcthulhu/stat

for any tilings of the plane T,S we write T->S if every finite patch of tiles in S occurs infinitely often in T.

(1) we first show that if T->T either T is periodic or there are uncountably many tilings

lets imagine building up a tiling S step by step (for concreteness in say, a square grid we can enumerate the squares in a spiral around the origin and say at each stage we're adding a tile to cover the uncovered square with the smallest number, so we reach everywhere eventually)

we also want T->S
we say a "decision" happens when there is more than one way to extend our tiling so that it appears in T (and thus appears in T infinitely many times)

Follow

(note that we're talking about extending the tiling to *cover a particular square*, so all the ways of extending are mutually exclusive + exhaustive)

Sign in to participate in the conversation
Mastodon

a Schelling point for those who seek one