Ltac npe_simpl := rewrite ?NPEmul_ok, ?NPEpow_ok, ?PEpow_mul_l.Ltac npe_ring := intro l; simpl; ring.

(* Specifications: *)
Theorem isIn_ok e1 p1 e2 p2 : match isIn e1 p1 e2 p2 with | Some(n, e3) => let n' := ZtoN (Zpos p1 - NtoZ n) in (e2 ^ N.pos p2 === e1 ^ n' * e3)%poly /\ (Zpos p1 > NtoZ n)%Z | _ => True end.