Nice exposition. It does not mention the fact that this can also be used as a proof for the question whether an infinite plane can be tiled with a certain set o

Nice exposition. It does not mention the fact that this can also be used as a proof for the question whether an infinite plane can be tiled with a certain set of wang-tiles is undecidable. https://en.wikipedia.org/wiki/Wang_tile#Domino_problem https://en.wikipedia.org/wiki/Wang_tile#Domino_problem : "In 1966, Berger solved the domino problem in the negative. He proved that no algorithm for the problem can exist, by showing how to translate any Turing machine into a set of Wang tiles that tiles the plane if and only if the Turing machine does not halt. The undecidability of the halting problem (the problem of testing whether a Turing machine eventually halts) then implies the undecidability of Wang's tiling problem."