Trigger using function written in PL/PGSQL returns "Unrecognized language specified"

I am writing my first trigger & function.

First question:
---------------
I can't get psql to take the function declaration.

ds=# > CREATE FUNCTION trigger_insert_update_copay()
ds-# RETURNS opaque

ds-# RETURNS opaque AS 'BEGIN
ds'# new.copay = (new.allowable * new.percent);
ds'# RETURN new;
ds'# END;'
ds-# LANGUAGE 'plpgsql'
ds-# Error: ERROR: Unrecognized language specified in a CREATE FUNCTION:
'plpgsql'. Recognized languages are sql, C, internal and the created
procedural languages.

Here is my function:
CREATE FUNCTION trigger_insert_update_copay()
RETURNS opaque -- should this be NUMERIC(??) or FLOAT4?
AS 'BEGIN
new.copay = (new.allowable * new.percent);
RETURN new;
END;'
LANGUAGE 'plpgsql';

Here is my Trigger:
CREATE TRIGGER trigger_copay
BEFORE INSERT
ON coverage
FOR EACH ROW
EXECUTE PROCEDURE trigger_insert_update_copay();

Second question:
----------------
It is supposed to multiply the 'allowable' and 'percent' field and leave
the result in 'copay'. Is
new.copay = (new.allowable * new.percent);
RETURN new;
The correct code to do that?

Dan Browning, Cyclone Computer Systems, danb(at)cyclonecomputers(dot)com