proposition: Lemma toNat_low n1 n2 (p: BITS (n1+n2)) : toNat (low n1 p) = toNat p %% 2^n1.
proof: Proof. by rewrite -{1}(toNatK p) low_fromNat toNat_fromNat. 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