Proof with simpl_env; eauto.
intros E F x U T H.
remember (F ++ x ~ bind_typ U ++ E) as G.
generalize dependent F.
induction H; intros F Heq; subst...
Case "wf_typ_var".
analyze_binds H...
Case "wf_typ_all".
pick fresh Y and apply wf_typ_all...
rewrite <- app_assoc.
apply H1...
Qed.

(* Specifications: *)
Lemma wf_typ_subst_tb : forall F Q E Z P T,
wf_typ (F ++ Z ~ bind_sub Q ++ E) T ->
wf_typ E P ->
uniq (map (subst_tb Z P) F ++ E) ->
wf_typ (map (subst_tb Z P) F ++ E) (subst_tt Z P T).