proposition: Lemma toZp_dropmsb n (p: BITS n.+2) : toZp (n:=n.+1) (dropmsb p) = toZpAux (m:=n.+1) p.
proof: Proof. apply val_inj. rewrite /toZp/toZpAux/= Zp_cast; last apply pow2_gt1. rewrite toNat_dropmsb. by rewrite modn_mod. Qed.
imports: Coq(ZArith.ZArith) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq fintype tuple div zmodp ssralg) ssrextra.nat ssrextra.tuple spec.spec