(* ----------------------------------------------------------------------------- *)

(* could also be an exists form *)
Lemma E_Pi2 : forall L G rho A B,
(∀ x : atom, x `notin` L → Typing ([(x, Tm A)] ++ G) (open_tm_wrt_tm B (a_Var_f x)) a_Star) ->
Typing G (a_Pi rho A B) a_Star.