Corollary wmsb_Zabs_pos:
  forall sz (w: word sz),
    wmsb w false = false -> Z.abs (wordToZ w) = wordToZ w.Corollary wmsb_Zabs_neg:
  forall sz (w: word sz),
    wmsb w false = true -> (Z.abs (wordToZ w) = - wordToZ w)%Z.

Lemma wmsb_false_wordToNat_eq: forall sz (w: word (S sz)), wmsb w false = false -> wordToNat w = wordToNat (split1 sz _ (eq_rect _ word w _ (Nat.add_comm 1 sz))).