Definition agree32 (a: Ptrofs.int) (b: Int.int) : Prop :=
  Ptrofs.unsigned a = Int.unsigned b.

Lemma agree32_sub: forall a1 b1 a2 b2, agree32 a1 b1 -> agree32 a2 b2 -> agree32 (Ptrofs.sub a1 a2) (Int.sub b1 b2).