>>> list(filter(is_symmetric, all_relations(3)))
[[(0, 0, 0), (0, 0, 0), (0, 0, 0)], [(0, 0, 0), (0, 0, 0), (0, 0, 1)], [(0, 0, 0), (0, 0, 1), (0, 1, 0)], [(0, 0, 0), (0, 0, 1), (0, 1, 1)], [(0, 0, 0), (0, 1, 0), (0, 0, 0)], [(0, 0, 0), (0, 1, 0), (0, 0, 1)], [(0, 0, 0), (0, 1, 1), (0, 1, 0)], [(0, 0, 0), (0, 1, 1), (0, 1, 1)], [(0, 0, 1), (0, 0, 0), (1, 0, 0)], [(0, 0, 1), (0, 0, 0), (1, 0, 1)], [(0, 0, 1), (0, 0, 1), (1, 1, 0)], [(0, 0, 1), (0, 0, 1), (1, 1, 1)], [(0, 0, 1), (0, 1, 0), (1, 0, 0)], [(0, 0, 1), (0, 1, 0), (1, 0, 1)], [(0, 0, 1), (0, 1, 1), (1, 1, 0)], [(0, 0, 1), (0, 1, 1), (1, 1, 1)], [(0, 1, 0), (1, 0, 0), (0, 0, 0)], [(0, 1, 0), (1, 0, 0), (0, 0, 1)], [(0, 1, 0), (1, 0, 1), (0, 1, 0)], [(0, 1, 0), (1, 0, 1), (0, 1, 1)], [(0, 1, 0), (1, 1, 0), (0, 0, 0)], [(0, 1, 0), (1, 1, 0), (0, 0, 1)], [(0, 1, 0), (1, 1, 1), (0, 1, 0)], [(0, 1, 0), (1, 1, 1), (0, 1, 1)], [(0, 1, 1), (1, 0, 0), (1, 0, 0)], [(0, 1, 1), (1, 0, 0), (1, 0, 1)], [(0, 1, 1), (1, 0, 1), (1, 1, 0)], [(0, 1, 1), (1, 0, 1), (1, 1, 1)], [(0, 1, 1), (1, 1, 0), (1, 0, 0)], [(0, 1, 1), (1, 1, 0), (1, 0, 1)], [(0, 1, 1), (1, 1, 1), (1, 1, 0)], [(0, 1, 1), (1, 1, 1), (1, 1, 1)], [(1, 0, 0), (0, 0, 0), (0, 0, 0)], [(1, 0, 0), (0, 0, 0), (0, 0, 1)], [(1, 0, 0), (0, 0, 1), (0, 1, 0)], [(1, 0, 0), (0, 0, 1), (0, 1, 1)], [(1, 0, 0), (0, 1, 0), (0, 0, 0)], [(1, 0, 0), (0, 1, 0), (0, 0, 1)], [(1, 0, 0), (0, 1, 1), (0, 1, 0)], [(1, 0, 0), (0, 1, 1), (0, 1, 1)], [(1, 0, 1), (0, 0, 0), (1, 0, 0)], [(1, 0, 1), (0, 0, 0), (1, 0, 1)], [(1, 0, 1), (0, 0, 1), (1, 1, 0)], [(1, 0, 1), (0, 0, 1), (1, 1, 1)], [(1, 0, 1), (0, 1, 0), (1, 0, 0)], [(1, 0, 1), (0, 1, 0), (1, 0, 1)], [(1, 0, 1), (0, 1, 1), (1, 1, 0)], [(1, 0, 1), (0, 1, 1), (1, 1, 1)], [(1, 1, 0), (1, 0, 0), (0, 0, 0)], [(1, 1, 0), (1, 0, 0), (0, 0, 1)], [(1, 1, 0), (1, 0, 1), (0, 1, 0)], [(1, 1, 0), (1, 0, 1), (0, 1, 1)], [(1, 1, 0), (1, 1, 0), (0, 0, 0)], [(1, 1, 0), (1, 1, 0), (0, 0, 1)], [(1, 1, 0), (1, 1, 1), (0, 1, 0)], [(1, 1, 0), (1, 1, 1), (0, 1, 1)], [(1, 1, 1), (1, 0, 0), (1, 0, 0)], [(1, 1, 1), (1, 0, 0), (1, 0, 1)], [(1, 1, 1), (1, 0, 1), (1, 1, 0)], [(1, 1, 1), (1, 0, 1), (1, 1, 1)], [(1, 1, 1), (1, 1, 0), (1, 0, 0)], [(1, 1, 1), (1, 1, 0), (1, 0, 1)], [(1, 1, 1), (1, 1, 1), (1, 1, 0)], [(1, 1, 1), (1, 1, 1), (1, 1, 1)]]
>>> len(_)
64