It is doing my head in

Ok all here is an question for you.

I am running pgsql on a linux 5.1 box.

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postgres=> create table smile (
postgres-> s1 integer,
postgres-> s2 integer );
CREATE
postgres=> insert into smile values ( 1 , 2 );
INSERT 17866 1
postgres=> insert into smile values ( 3 , 4 );
INSERT 17867 1
postgres=> select * from smile
postgres-> ;
s1|s2
--+--
1| 2
3| 4
(2 rows)

postgres=> create function ttt() returns integer
postgres-> as 'select 4 as result'
postgres-> language 'sql' ;
CREATE
postgres=> select * from smile where s2=ttt() ;
s1|s2
--+--
3| 4
(1 row)

postgres=> create trigger trg1 after insert on smile for each row
postgres-> execute procedure ttt() ;
ERROR: CreateTrigger: function ttt () does not exist
postgres=> \q

So my question is - why does the create trigger function fail when the
function does in
fact exist ?

Andrew