func (q *Rat) Mul(x, y *Rat) *Rat {
x.doinit()
y.doinit()
q.doinit()
C.mpq_mul(&q.i[0], &x.i[0], &y.i[0])
return q
}
// Mul sets z to the product x*y and returns z.
func (z *Rat) Mul(x, y *Rat) *Rat {
x.doinit()
y.doinit()
z.doinit()
C.mpq_mul(&z.i[0], &x.i[0], &y.i[0])
return z
}