Fixpoint extend {A} (l : list A) ls :=
  match l, ls with
  | x :: xs, y :: ys => (x :: y) :: extend xs ys
  | _, _ => ls
  end.

Lemma semax_body_mono : forall V G {cs : compspecs} f s V2 G2 (HV : incl V V2) (HG : incl G G2) (Hdistinct : NoDup (map fst V2 ++ map fst G2)), semax_body V G f s -> semax_body V2 G2 f s.