fact: Definition zeroTruncate extra {n} (p: BITS (n + extra)) : option (BITS n) := let (hi,lo) := split2 extra _ p in if hi == zero _ then Some lo else None.
imports: Coq(ZArith.ZArith Strings.String) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq fintype tuple zmodp)