Что выведет код?

def f(seq):
    if not seq:
        yield seq
    else:
        for i in range(len(seq)):
            rest = seq[:i] + seq[i+1:]
            for x in f(rest):
                yield seq[i:i+1] + x
a = [*f(['a', 'b'])]
b = [*f(['a', 'b', 'c', 'd'])]
print(a, len(b))