return [ [ 2, 3, 4, 5 ], [ 1, 6, 7, 8 ], [ 1, 8, 9, 10 ], [ 1, 10, 11, 12 ], 
  [ 1, 12, 13, 6 ], [ 2, 5, 14, 7 ], [ 2, 6, 14, 15 ], [ 2, 15, 9, 3 ], 
  [ 3, 8, 16, 17 ], [ 3, 17, 11, 4 ], [ 4, 10, 17, 18 ], [ 4, 18, 13, 5 ], 
  [ 5, 12, 16, 14 ], [ 6, 13, 15, 7 ], [ 7, 14, 16, 8 ], [ 9, 15, 13, 18 ], 
  [ 9, 18, 11, 10 ], [ 11, 17, 16, 12 ] ];
