Ltac headptr_field_compatible :=
  match goal with H: headptr ?P |- field_compatible _ _ ?P =>
  apply headptr_field_compatible;
        [ apply H | reflexivity | | simpl; computable | apply la_env_cs_sound; reflexivity];
    apply compute_legal_nested_field_spec';
    simpl_compute_legal_nested_field;
    repeat apply Forall_cons; try apply Forall_nil
  end.

Lemma data_at_type_changable {cs}: forall (sh: Share.t) (t1 t2: type) v1 v2, t1 = t2 -> JMeq v1 v2 -> @data_at cs sh t1 v1 = data_at sh t2 v2.