Mixing properties of colourings of the ℤ^dlattice

We study and classify proper q-colourings of the ℤd lattice, identifying three regimes where different combinatorial behaviour holds. (1) When q ≤ d + 1, there exist frozen colourings, that is, proper q-colourings of ℤd which cannot be modified on any finite subset. (2) We prove a strong list-colouring property which implies that, when q ≥ d+2, any proper q-colouring of the boundary of a box of side length n ≥ d + 2 can be extended to a proper q-colouring of the entire box. (3) When q ≥ 2d+1, the latter holds for any n ≥ 1. Consequently, we classify the space of proper q-colourings of the ℤd lattice by their mixing properties.