fact: Fixpoint fromNat {n} m : BITS n := if n is _.+1 then joinlsb (fromNat m./2, odd m) else nilB.
imports: Coq(ZArith.ZArith Strings.String) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq fintype tuple zmodp)