then one identifies the square at (x , y) E JR2 with the squares at (x + i , y + j) , for all (i , j) E 'Z}. The board centered at (0, 0) is a fundamental domain [54] for the 'Z} action. Every chess piece on the torus board is thus represented by infinitely many replicas, each in the corresponding position on its tile/board. (FIGURE 6 depicts the torus with a queen and a knight.)