adds a link from this thing to other thing
        using type (is_a, has_a, uses, contains, part_of)

def links_to(self, other, tpe):
        """
        adds a link from this thing to other thing
        using type (is_a, has_a, uses, contains, part_of)
        """
        if self.check_type(tpe):
            self.links.append([other, tpe])
        else:
            raise Exception('aikif.core_data cannot process this object type')