proposition: Lemma fv_exp_open_exp_wrt_exp_rec_upper_mutual : (forall e1 e2 n1, fv_exp (open_exp_wrt_exp_rec n1 e2 e1) [<=] fv_exp e2 `union` 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