“…, where all sets on the right side are non-empty. (If V = V i ,a 1 ∪V i ,a ′ 1 for every i ∈ [4], then V = U (Q ) and there is nothing to prove.) Since, by Corollary 2, for every j ∈ {2, ..., k }, the codes V i ,a j i c and V i ,a ′ j i c are strongly equivalent, we may pass by gluing and cutting from V to a cube tiling code V , where V = V i ,a 1 ∪ V i ,a ′ 1 (compare Subsection 2.2).…”