Using UNION inside a cursor

Dear Friends,

I am working on Postgresql 7.3.4 on RH Linux Server 7.3.

I have problem in executing the following procedure

CREATE OR REPLACE FUNCTION list_history()
RETURNS refcursor AS
'DECLARE
ref REFCURSOR;
BEGIN
OPEN ref FOR
(SELECT * FROM history WHERE obs_type = \'AA\' )
UNION
(SELECT * FROM history WHERE obs_type = \'TA\');

RETURN ref;
END;'
LANGUAGE 'plpgsql' VOLATILE;

While executing this I got the following error

WARNING: plpgsql: ERROR during compile of list_history near line 5
ERROR: syntax error at "("

While I execute the following code it is working fine and fetches values.
(SELECT * FROM history WHERE obs_type = \'AA\' )
UNION
(SELECT * FROM history WHERE obs_type = \'TA\');

Where I am wrong. Please shed some light,

Regards
Kumar