Hint Resolve subst_exp_fresh_eq : lngen.
Hint Rewrite subst_exp_fresh_eq using solve [auto] : lngen.
(* begin hide *)

Lemma subst_exp_fresh_same_mutual :
(forall e2 e1 x1,
x1 `notin` fv_exp e1 ->
x1 `notin` fv_exp (subst_exp e1 x1 e2)).