def single(args, kwds):
    """Return a true value only when a unique argument is given.

    When needed, the most suitable result will be wrapped using the
    `~xotl.tools.fp.option.Maybe`:class:.

    .. versionadded:: 1.8.0

    """
    from xotl.tools.fp.option import Just, Wrong, take
    if len(args) == 1 and not kwds:
        res = take(args[0])
        if not res:
            res = Just(res)
        res = Just(res)
    elif not args and len(kwds) == 1:
        res = kwds
    else:
        res = Wrong((args, kwds))
    return res
