def intersect(seq1, seq2):
    res = []                     # start with an empty list
    for x in seq1:               # scan the first sequence
        if x in seq2:
            res.append(x)        # add common items to end
    return res

def union(seq1, seq2):
    res = map(None, seq1)        # copy of seq1 (see ch13)
    for x in seq2:               # add new items in seq2
        if not x in res:
            res.append(x)
    return res