CZ = [ [set([1,2,3,4]),
       set([5,6,7,8]),
       set([9,10,11,12]),
       set([13,14,15,16])],

      [set([1,5,9,13]),
       set([2,6,10,14]),
       set([3,7,11,15]),
       set([4,8,12,16])],
      [set([1,6,11,16]),
       set([2,7,12,13]),
       set([3,8,9,14]),
       set([4,5,10,15])]
     ]

column = [
           [1,2,3,4],
           [5,6,7,8],
           [9,10,11,12],
           [13,14,15,16]
         ]

for t in xrange(2):
        for r in xrange(4):
                R=set()
                for C in column:
                        for c in C:
                                R.add(c)