Instance LS: listspec t_struct_list _tail.Definition Vprog : varspecs := nil.Definition isptrb v :=
   match v with | Vptr _ _ => true | _ => false end.Definition Igt a b:=
Int.cmp Cgt a b = true.Definition fst_3 {A B C} (a: A* B*C) := fst (fst a).Definition snd_3 {A B C} (a: A * B * C) := snd (fst a).Definition third_3 {A B C} (a: A * B * C) := snd a.

Qed. Lemma Forall_app : forall {A} P (l1 l2 :list A