Polyboxes, cube tilings and rigidity

Abstract

A non-empty subset A of X = X_1 x...x X_d is a (proper) box if A = A_1 x...x A_d and A_i is a (proper) subset of X_i for each i. Suppose that for each pair of boxes A, B and each i, one can only know which of the three states takes place: A_i = B_i, A_i = X_i\setminus B_i, A_i is different from each of the sets B_i, X_i\setminus B_i. Let F and G be two systems of disjoint boxes. Can one decide whether their unions are equal? In general, the answer is no, but as is shown in the paper, it is yes if both systems consist of pairwise dichotomous boxes. Several criteria that enable to compare such systems are collected. The paper includes also rigidity results, which say what assumptions have to be imposed on F to ensure that \bigcup F = \bigcup G implies F = G. As an application, the rigidity conjecture for 2-extremal cube tilings of Lagarias and Shor is verified.