(** C allows pointers one past the last element of an array.  These are not
  valid according to the previously defined [valid_pointer]. The property
  [weak_valid_pointer m b ofs] holds if address [b, ofs] is a valid pointer
  in [m], or a pointer one past a valid block in [m].  *)

Definition weak_valid_pointer (m: mem) (b: block) (ofs: Z) :=
  valid_pointer m b ofs || valid_pointer m b (ofs - 1).

Lemma weak_valid_pointer_spec: forall m b ofs, weak_valid_pointer m b ofs = true <-> valid_pointer m b ofs = true \/ valid_pointer m b (ofs - 1) = true.