“…The proof that every tiling enforced by the matching rules of these tiles is aperiodic follows from the necessity of arranging the tiles such that larger and larger squares are defined by the patterns on the tiles, (shown in gray in Figure 2). The emerging patterns may be described as quasiperiodic (Durand, 1999), self-similar (Lafitte & Weiss, 2008a), or hierarchical (Lafitte & Weiss, 2008a; Goodman-Strauss, 1999), and contain squares whose edges are defined by 2 n + 1 tiles at the n -th level in the hierarchy. Further experimentation with the tiles of Figure 1 demonstrates that, within the Wang tiling system, it is easy to make errors by adding tiles at random according to the edge matching rules, creating untilable regions.…”