a = {1,2,3,4}
b = {4,5}

a.intersect(b)   # {4}
a & b            # {4}

a.union(b)       # {1,2,3,4,5}
a | b            # {1,2,3,4,5}

a.difference(b)  # {1,2,3}
a - b            # {1,2,3}