x1 = [1, 2;
      3, 4];
x2 = [2, 4;
      1, 3];
x3 = [4, 3;
      2, 1];
x4 = [3, 1;
      4, 2];

(rot90 (x1)== x2 && rot90 (x1, 2) == x3 && rot90 (x1, 3) == x4
 && rot90 (x1, 4) == x1 && rot90 (x1, 5) == x2 && rot90 (x1, -1) == x4)
