proposition: Lemma shrBn_Sn : forall n b (bs: BITS n) k, shrBn [tuple of b :: bs] k.+1 = shrBn (joinmsb0 bs) k.
proof: Proof. move=> n b S k. by rewrite {1}/shrBn iterSr //= /droplsb //= tuple.beheadCons. Qed.
imports: HB(structures) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq fintype tuple zmodp div) ssrextra.tuple ssrextra.nat spec spec.properties operations mathcomp(ssralg)