(** [valid_pointer m b ofs] returns [true] if the address [b, ofs] is nonempty in [m] and [false] if it is empty. *)
Parameter valid_pointer: forall (m: mem) (b: block) (ofs: Z), bool.

Axiom valid_pointer_nonempty_perm:
forall m b ofs,
valid_pointer m b ofs = true <-> perm m b ofs Cur Nonempty.