add foreign key constraint after table creation?

I have two tables both of which have foreign key constraints on each
other. I presume I won't get into a deadlock situation... people can be
made independantly of objects, but if a person object is made this is
recorded in n_object_id.

My problem is that I cannot load my full table schema using \i as to
define peopel I need objects defined and vice versa. To get around this
I though I could define the foreign key constraint on people.n_object_id
after I had loaded everything. How do I do it? The alter table \h
command isn't very helpful!

CREATE TABLE people (
    n_id SERIAL PRIMARY KEY,
    n_object_id INTEGER DEFAULT NULL
                            references objects
                            ON UPDATE CASCADE
                            ON DELETE SET NULL,
    n_objects_counter INTEGER DEFAULT 0,
    b_hidden BOOLEAN DEFAULT false,
    dt_created TIMESTAMP DEFAULT current_timestamp,
    dt_modified TIMESTAMP DEFAULT current_timestamp,
    t_nickname VARCHAR(20) UNIQUE NOT NULL,
    t_firstname VARCHAR(20) NOT NULL,
    t_surname VARCHAR(25) NOT NULL,
    t_mobile VARCHAR(15) UNIQUE,
    t_email VARCHAR(30) UNIQUE,
    b_registered BOOLEAN DEFAULT false,
    n_email_status INT2 DEFAULT 0,
    n_txt_status INT2 DEFAULT 0,
    b_work_hours BOOLEAN DEFAULT false
);

CREATE TABLE objects (
    n_id SERIAL PRIMARY KEY,
    t_text_id VARCHAR(25) UNIQUE NOT NULL,
    b_hidden BOOLEAN DEFAULT false,
    dt_created TIMESTAMP DEFAULT current_timestamp,
    dt_modified TIMESTAMP DEFAULT current_timestamp,
    n_creator INTEGER NOT NULL
                       references people
                       ON UPDATE CASCADE
                       ON DELETE CASCADE,
    n_type INT2 NOT NULL DEFAULT 0,
    t_name VARCHAR(30) NOT NULL,
    t_description VARCHAR(200),
    t_location VARCHAR(100) DEFAULT NULL,
    t_postcode VARCHAR(10) DEFAULT NULL,
    n_id_photo INTEGER DEFAULT NULL
                       references photo
                       ON UPDATE CASCADE
                       ON DELETE SET NULL

);
...

--
Rory Campbell-Lange
<rory@campbell-lange.net>
<www.campbell-lange.net>