Stored Procedures and Return Type

Hello,

What would be the rtype for a function to return tuples selected over more
than one table? The closest I can find is setof but this rtype is for all
columns of only one table.

Example:

states
state_id integer
state_name varchar
state_abbreviation char(2)

districts
district_id integer
state_id integer
district_name varchar

CREATE OR REPLACE FUNCTION districts(varchar, varchar) RETURNS ???? AS '
SELECT state_name, districtname FROM states s, districts d
WHERE s.state_id = d.state_id AND s.state_name = $1 AND d.district_name = $2;
' LANGUAGE 'sql';