proposition: Lemma getBit_high n1: forall n2 (p: BITS (n1+n2)) i, getBit (high n2 p) i = getBit p (i+n1).
proof: Proof. induction n1 => // n2 p i. by rewrite addn0. rewrite addnS. case/tupleP: p => [b p]. apply IHn1. 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