mp_exch
mp_exch(&q, c);
mp_exch(&x, d);
mp_exch(&t, c);
mp_exch(&D, c);
mp_exch(&C, c);
mp_exch(&q, c);
mp_exch(&t, c);
mp_exch(&t, c);
mp_exch(&t, b);
mp_exch(&res, Y);
mp_exch(&res, Y);
mp_exch(&q, c);
mp_exch(&u, &v);
mp_exch(a, b);
mp_exch(&t, d);