Cube tilings, partition counters, and the Calkin--Wilf and Kepler trees

Abstract

A tiling of the integer lattice ${\mathbb{Z}}^d$ by translates of the discrete cube $K_d=\{0,1{\}}^d$ cuts every translate $K_d+x$ into subcubes. We study the function $\ell (x)$ counting these parts. Its sum over every translate of $K_d$ equals $3^d$, for an arbitrary translation set. For lattice tilings with a triangular basis we obtain a dimension-reduction formula, and we describe every cocyclic lattice by a single normalized congruence. Along a cyclic generator, the counter of a signed bidiagonal lattice is a row of Stern's diatomic sequence; pairs of counter values realize the Calkin--Wilf tree, and complementary binary words realize the Kepler tree. For the binary lattice, the translated counter labelings of the cube carry generating face partitions, supplied by the tiling itself, which force the levels of the Kepler tree, and every nontrivial face partition has a unique lamination direction. Using finite Fourier analysis we prove that the ordered cyclic profile determines a standard cocyclic cube tiling lattice up to coordinate reflections. For lattices tiling by discrete boxes we determine exactly when the analogous statement holds.

arXiv comment23 pages, 7 figures