How to use the multimethod.__init__.subtype function in multimethod

def __new__(cls, types: Iterable):
        return tuple.__new__(cls, map(subtype, types))

def __eq__(self, other):
        return isinstance(other, subtype) and self.__getstate__() == other.__getstate__()

def get_type(arg: Iterable):
    """Return generic type checking first value."""
    return subtype(type(arg), *map(get_type, itertools.islice(arg, 1)))