'Remove first matching item in list.
:param item:        An aspectclass
:raises ValueError: When to be removed item is not found in list.'

def _remove(self, item):

    for aspect in self:
        if ((aspect is item) or isinstance(aspect, item)):
            return super().remove(aspect)
    raise ValueError('{}._remove(x):    {}    not    in    list.'.format(type(self).__name__, item))
