proposition: Lemma fv_exp_subst_exp_fresh_mutual : (forall e1 e2 x1, x1 `notin` fv_exp e1 -> fv_exp (subst_exp e2 x1 e1) [=] fv_exp e1).
proof: Proof. apply_mutual_ind exp_mutind; default_simp; fsetdec. Qed.
imports: Coq.Logic.FunctionalExtensionality Coq.Program.Equality Metalib.Metatheory Metalib.LibLNgen Stlc