Trigger Error!

Hi!

I've postgresql 6.5.3 system and 50 tables, but i need to run this
trigger: (the comments are in spanish :-) )

create function gen_req() returns opaque as '
declare
cantdisp int4;
suma int4;
cantprodsol int4;
codereq int4;

begin
if int4ne(new.candisproter, old.candisproter) then
select candisproter into cantdisp from proter
where codproter=new.codproter;

if not found then
raise exception ''No hay datos de productos'';
end if;

select sum(stomin) into suma from almproterpt
where codproter=new.codproter;

if not found then
raise exception ''No hay datos de Stocks minimos'';
end if;

cantprodsol := old.candisproter - new.candisproter;

if int4le((cantdis - cantprodsol), suma) then
select codreq from requisicion
where fecsalreq=current_date;
if not found then
--se inserta la requisicion;
insert into requisicion(fecsalreq,codest)
values(current_date,1);
end if;
--se repite la query pero asignando el valor;
select codreq into codereq from requisicion
where fecsalreq=current_date;
--procedemos a insertar el detalle;
insert into detallereq(codreq,codpt,canpt)
values(codereq,new.codproter,cantprodsol);
end if;
end if;
return new;
end;
' language 'plpgsql';

create trigger gen_req_tg before update on proter for each row execute
procedure gen_req();

Well, the trigger is created, the trigger should intercepts the update
event in table 'proter' and when I reduce the 'candisproter' field to
specied value then, the trigger is fired. But.........

It isn't work, when I run the update operation, then, I give this error:

'There is no operator '=$' for types 'int4' and 'int4' you will either
have to retype this query using and explicit cast, or you will have
to define the operator using CREATE OPERATOR'

I don't understand what's the meaning af this message, the types are
incorrect?? WHAT'S WRONG?????

thankx!!!