proposition: Lemma addp1 p : xI p = (xO p + 1)%N :> nat.
proof: Proof. by rewrite addn1. Qed.
imports: ZArith Ncring Ncring_tac mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype) mathcomp(div finfun bigop prime binomial ssralg finset fingroup finalg) mathcomp(perm zmodp matrix) ssralg_ring_tac