(** Expressing 64-bit operations in terms of 32-bit operations *)

Lemma decompose_sub':
forall xh xl yh yl,
sub (ofwords xh xl) (ofwords yh yl) =
ofwords (Int.add (Int.add xh (Int.not yh)) (Int.add_carry xl (Int.not yl) Int.one))
(Int.sub xl yl).