The Rule does not working.

Dear All,

Please help. I create below Deleted Rule in Postgres 7.1.3. But it does not
working. Please Help. That mean when I delete the record but it does not
update the table by the update command.

CREATE RULE inv_so_delete1 AS ON DELETE TO inv_detail DO UPDATE so_info SET
l_invoice = 'f'::bool WHERE ((NOT (EXISTS (SELECT inv_detail.c_sorder FROM
inv_detail WHERE (inv_detail.c_sorder = old.c_sorder)))) AND
(so_info.c_sorder = old.c_sorder));

Thanks

King King