<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 async def remove(self, *instances, using_db=None) -> None: """ Removes one or more of ``instances`` from the relation. """

        db = using_db if using_db else self.model._meta.db
        if not instances:
            raise OperationalError("remove() called on no instances")
        through_table = Table(self.field.through)

        if len(instances) == 1:
            condition = (getattr(through_table, self.field.forward_key) == instances[0].id) & (
                getattr(through_table, self.field.backward_key) == self.instance.id
            )
        else:
            condition = (getattr(through_table, self.field.backward_key) == self.instance.id) & (
                getattr(through_table, self.field.forward_key).isin([i.id for i in instances])
            )
        query = db.query_class.from_(through_table).where(condition).delete()
        await db.execute_query(str(query))