def _muly(p, x, y):
    'Returns ``_mexpand(y**deg*p.subs({x:x / y}))``.'
    (p1,) = parallel_poly_from_expr((p,), x)[0]
    n = degree(p1)
    a = [((c * (x ** i)) * (y ** (n - i))) for ((i,), c) in p1.terms()]
    return Add(*a)
Returns ``_mexpand(y**deg*p.subs({x:x / y}))``.
def _muly(p, x, y):
    
    (p1,) = parallel_poly_from_expr((p,), x)[0]
    n = degree(p1)
    a = [((c * (x ** i)) * (y ** (n - i))) for ((i,), c) in p1.terms()]
    return Add(*a)