return [ [ [ 2, 3, 4, 5 ], [ 1, 5, 6, 7 ], [ 1, 7, 8, 4 ], [ 1, 3, 9, 5 ], 
      [ 1, 4, 9, 2 ], [ 2, 9, 8, 7 ], [ 2, 6, 8, 3 ], [ 3, 7, 6, 9 ], 
      [ 4, 8, 6, 5 ] ] ];