pg with different sql?

Hi all,

I'm new to postgres and I'm doing a database project for a
subject at college in postgres. I've studied databases using
DataBases Management Systems by Ramakrishnan.
I've done some create tables and at psql interactive prompt I've
done:
\i proj.sql
(where proj.sql is the filename with the CREATE TABLEs)

AFAIK, SQL is standard and should be the same for all DBMSs.

For example:
CREATE TABLE socio (id integer SERIAL PRIMARY KEY,nome varchar,alcunha string,data_filiacao date)

CREATE TABLE paga_cota (ano integer,mes integer,valor integer,id integer,PRIMARY KEY(id,ano,mes),FOREIGN KEY(id)
REFERENCES(socio))


After this I get an error around CREATE (of the 2nd table). I
just can't imagine what it might be. 

I'd appreciate your help.

TIA,
My best regards,
-- 
Paulo J. Matos : pocm(_at_)rnl.ist.utl.pt
Instituto Superior Tecnico - Lisbon    
Software & Computer Engineering - A.I.- > http://www.rnl.ist.utl.pt/~pocm ---    Yes, God had a deadline...    So, He
wroteit all in Lisp!