return [ [ 2, 3, 4, 5 ], [ 1, 6, 7, 8 ], [ 1, 8, 9, 4 ], [ 1, 3, 10, 11 ], 
  [ 6, 6, 1, 11 ], [ 5, 5, 12, 2 ], [ 2, 12, 13, 14 ], [ 14, 14, 3, 2 ], 
  [ 3, 14, 13, 10 ], [ 15, 15, 4, 9 ], [ 4, 15, 12, 5 ], [ 6, 11, 13, 7 ], 
  [ 7, 12, 15, 9 ], [ 8, 8, 7, 9 ], [ 10, 10, 13, 11 ] ];
