a = set([1,2,3,4])
b = set([3,4,5,6])
print(a.intersection(b)) # 交集 {3, 4}
print(a.union(b)) # 并集 {1, 2, 3, 4, 5, 6}
print(a.difference(b)) # 差集 in a but not in b {1, 2}
print(b.difference(a)) # 差集 in b but not in a {5, 6}
print(a.symmetric_difference(b)) # 对称 差集 {1, 2, 5, 6}
