'n - p1 with n convertible to the coefficient domain.
Examples
>>> from sympy.polys.domains import ZZ
>>> from sympy.polys.rings import ring
>>> _, x, y = ring(\'x, y\', ZZ)
>>> p = x + y
>>> 4 - p
-x - y + 4'

def __rsub__(p1, n):

    ring = p1.ring
    try:
        n = ring.domain_new(n)
    except CoercionFailed:
        return NotImplemented
    else:
        p = ring.zero
        for expv in p1:
            p[expv] = (- p1[expv])
        p += n
        return p
