HOWTO return a resultset form SP

Hi All
I tried to write a Stored Procedure that
returns a resultset that contains data of more then
on table.
My prob is that i don't know how to declate the return
type
e.g:
CREATE FUNCTION getoffers()
RETURNS SETOF ??????
AS
'SELECT
persistent.coid,persistent.classname,serviceoffer.range_begin,serviceoffer.r
ange_end,serviceoffer.coid_service,productoffer.coid_price,productoffer.coid
_quantity
FROM persistent,productoffer,serviceoffer,genericservice WHERE
productoffer.coid=serviceoffer.coid AND serviceoffer.coid=persistent.coid
AND serviceoffer.coid_service=genericservice.coid'
LANGUAGE 'SQL';

Maybe someone can help me ?

Thanx Thorsten