problem creating triggers and stored procedures

I'm trying to work out how to get triggers working, using the example
"add_one(int4)" C function given in the programmers guide;

postgres=# select add_one(-2.4) as stuff;
stuff
-------
-1
(1 row)

... so, it works fine. However, I can't create a trigger, using that
stored procedure;

postgres=# create trigger add_one_to_col_one AFTER INSERT on test_table for each row execute procedure add_one();
ERROR: CreateTrigger: function add_one() does not exist

Any idea why this would be ? Also, I created a user, and tryed to execute
the add_one() stored procedure. It seems normal users don't have access to
them. The following returns "add_one" when run as postgres, but not when
run as a normal user. Can this behaviour be altered ?

select proname from pg_proc where proname = 'add_one';

John

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_______________________________________
John Looney Chief Scientist
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