show_sdiff(record u, x)
{
    record r;
    text s;

    r.copy(u);

    for (s in x) {
        if (r.key(s)) {
            r.delete(s);
        } else {
            r.p_integer(s, 0);
        }
    }

    r.vcall(o_, 0, "\n");
}

new_set(...)
{
    record r;

    ucall(r_p_integer, 1, r, 0);

    r;
}

main(void)
{
    show_sdiff(new_set("John", "Bob", "Mary", "Serena"),
               new_set("Jim", "Mary", "John", "Bob"));

    0;
}