def __sub__(p1, p2):
        if not p2:
            return p1.copy()
        ring = p1.ring
        if isinstance(p2, ring.dtype):
            p = p1.copy()
            get = p.get
            zero = ring.domain.zero
            for k, v in p2.items():
                v = get(k, zero) - v
                if v:
                    p[k] = v
                else:
                    del p[k]
            return p
        elif isinstance(p2, PolyElement):
            if isinstance(ring.domain, PolynomialRing) and ring.domain.ring == p2.ring:
                pass
            elif isinstance(p2.ring.domain, PolynomialRing) and p2.ring.domain.ring == ring:
                return p2.__rsub__(p1)
            else:
                return NotImplemented

        try:
            p2 = ring.domain_new(p2)
        except CoercionFailed:
            return NotImplemented
        else:
            p = p1.copy()
            zm = ring.zero_monom
            if zm not in p1.keys():
                p[zm] = -p2
            else:
                if p2 == p[zm]:
                    del p[zm]
                else:
                    p[zm] -= p2
            return p
Build a check_precondition function that uses both the old precondition check as well as the new function fn
dataset/ETHPy150Open sympy/sympy/sympy/polys/rings.py/PolyElement.__sub__--crossover with--dataset/ETHPy150Open google/nogotofail/nogotofail/mitm/connection/handlers/preconditions.py/_build_precondition_join_fn