fact: Definition catB {n1 n2} (p1: BITS n1) (p2: BITS n2) : BITS (n2+n1) := cat_tuple p2 p1.
imports: Coq(ZArith.ZArith Strings.String) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq fintype tuple zmodp)