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 wordToNat_ge1: forall sz (a b: word sz), a >= b -> (wordToNat a >= wordToNat b)%nat.