question on function definitions/casts

ANyway, I have another question for you guys.

create function get_citation (int2, int2, int4)
returns SETOF varchar AS
'select citation from citations where aid=$1 and wid=$2 and byteloc=$3'
LANGUAGE 'SQL'

At one point I retrieved this function from my psql db (I've taken over
from someone else) and I'm now in a position where I need to enter it again.
I got it using pg_dump -s (on the kind suggestion of Tom when I asked back
then).

However, when I enter it now, it just doesn't seem to like it.

I get:

Text=# create function get_citation (int2, int2, int4)
Text-# returns SETOF varchar AS
Text-# 'select citation from citations where aid=$1 and wid=$2 and byteloc=$3'
Text-# LANGUAGE 'SQL';
ERROR: Unable to identify an operator '=$' for types 'int2' and 'int4'
You will have to retype this query using an explicit cast
Text=#

I'm guessing this is a difference from an upgrade to psql?

I'm using:
[1:08pm] stephanus ~> psql -V
psql (PostgreSQL) 7.1.3

would this be something like:

cast(aid as int2)=$1
or
(int2 aid)=$1

I've read through the stuff in
http://www.ca.postgresql.org/users-lounge/docs/7.2/postgres/typeconv-oper.html
but I'm still confused.

Thanks,
--Cindy