Ltac show_stopped :=
  let m' := fresh "m'" in
  let e' := fresh "e'" in
  let H := fresh "H" in
  right; intros [m' [e' H]]; inv H.

Lemma closed_Lam_subst: forall e x v, closed (Lam e) -> subst x v (Lam e) = Lam e.