 It is also known that "square" tori exist whenever "m" = "n" and even (for the odd case the resulting tori cannot be square).The smallest possible binary "square" de Bruijn torus, depicted above right, denoted as "(4,4;2,2)2" de Bruijn torus (or simply as "B2"), contains all "2×2" binary matrices.Apart from "translation", "inversion" (exchanging "0"s and "1"s) and "rotation" (by 90 degrees), no other "(4,4;2,2)2" de Bruijn tori are possible - this can be shown by complete inspection of all "216" binary matrices (or subset fulfilling constrains such as equal numbers of "0"s and "1"s) .