def METHOD_NAME():
    assert ed("", "") == 0
    assert ed("", "A") == 1
    assert ed("A", "B") == 1
    assert ed("A", "A") == 0
    assert ed("A", "AB") == 1
    assert ed("BA", "AB") == 2
    for s, t in STRING_PAIRS:
        assert ed(s, "") == len(s)
        assert ed("", s) == len(s)
        assert ed(s, t) == ed(t, s)