Definition compat_pointer_chunks (chunk1 chunk2: memory_chunk) : Prop :=
  match chunk1, chunk2 with
  | (Mint32 | Many32), (Mint32 | Many32) => True
  | (Mint64 | Many64), (Mint64 | Many64) => True
  | _, _ => False
  end.

Lemma perm_inj: forall f m1 m2 b1 ofs k p b2 delta, mem_inj f m1 m2 -> perm m1 b1 ofs k p -> f b1 = Some(b2, delta) -> perm m2 b2 (ofs + delta) k p.