def isomorphic(a, b):
    if len(a) != len(b):
        return False
    forward, reverse = {}, {}
    for x, y in zip(a, b):
        if x in forward and forward[x] != y:
            return False
        if y in reverse and reverse[y] != x:
            return False
        forward[x], reverse[y] = y, x
    return True