Definition pointer_range_overlap p n p' n' :=
  exists l l', val2adr p l /\ val2adr p' l' /\ range_overlap l n l' n'.

Lemma pointer_range_overlap_refl: forall p n1 n2, isptr p -> n1 > 0 -> n2 > 0 -> pointer_range_overlap p n1 p n2.