   # result = intersection([
        #     [1],
        #     [1],
        # ])
        # self.assertTrue(result == [1])

        # result = intersection([
        #     [1, 2],
        #     [1],
        # ])
        # self.assertTrue(result == [1])

        # result = intersection([
        #     [1, 2, 3],
        #     [1, 4, 5, 3],
        #     [1, 6, 7, 3]
        # ])
        # result.sort()
        # self.assertTrue(result == [1, 3])