def main((field, field) p, (field, field) q) -> (field, field) {
    field a = 42;
    field d = 21;

    field dpxpyqxqy = d * p.0 * p.1 * q.0 * q.1;

    return ((p.0 * q.1 + q.0 * p.1) / (1 + dpxpyqxqy), (q.0 * q.1 - a * p.0 * p.1) / (1 - dpxpyqxqy));
}