def diff(s1, s2):
    """
    Return a normalised Levenshtein distance between two strings.

    Distance is normalised by dividing the Levenshtein distance of the
    two strings by the max(len(s1), len(s2)).

    Examples:

        >>> text.diff("foo", "foo")
        0

        >>> text.diff("foo", "fooo")
        1

        >>> text.diff("foo", "")
        1

        >>> text.diff("1234", "1 34")
        1

    Arguments:

        s1 (str): Argument A.
        s2 (str): Argument B.

    Returns:

        float: Normalised distance between the two strings.
    """
    return levenshtein(s1, s2) / max(len(s1), len(s2))