record
union(record a, record b)
{
    record c;
    r_copy(c, a);
    r_wcall(b, r_add, 1, 2, c);
    return c;
}

record
intersection(record a, record b)
{
    record c;
    text s;
    for (s in a) {
        if (r_key(b, s)) {
            c[s] = 0;
        }
    }
    return c;
}

record
difference(record a, record b)
{
    record c;
    r_copy(c, a);
    r_vcall(b, r_resign, 1, c);
    return c;
}

integer
subset(record a, record b)
{
    integer e;
    text s;
    e = 1;
    for (s in a) {
        if (!r_key(b, s)) {
            e = 0;
            break;
        }
    }
    return e;
}

integer
equal(record a, record b)
{
    return subset(a, b) && subset(b, a);
}

integer
main(void)
{
    record a, b;
    text s;

    r_fit(a, "apple", 0, "cherry", 0, "grape", 0);
    r_fit(b, "banana", 0, "cherry", 0, "date", 0);

    s = "banana";

    o_(" ", s, " is ", r_key(a, s) ? "" : "not ", "an element of A\n");
    o_(" ", s, " is ", r_key(b, s) ? "" : "not ", "an element of B\n");

    r_vcall(union(a, b), o_, 1, " ");
    o_newline();

    r_vcall(intersection(a, b), o_, 1, " ");
    o_newline();

    r_vcall(difference(a, b), o_, 1, " ");
    o_newline();

    o_(" ", subset(a, b) ? "yes" : "no", "\n");

    o_(" ", equal(a, b) ? "yes" : "no", "\n");

    return 0;
}