Proof with simpl_env; try solve [auto | intuition auto].
intros E e T H; induction H...
Case "typing_var".
repeat split...
eauto using wf_typ_from_binds_typ.
Case "typing_abs".
pick fresh y.
destruct (H0 y) as [Hok [J K]]...
repeat split. inversion Hok...
SCase "Second of original three conjuncts".
pick fresh x and apply expr_abs.
eauto using type_from_wf_typ, wf_typ_from_wf_env_typ.
destruct (H0 x)...
SCase "Third of original three conjuncts".
apply wf_typ_arrow; eauto using wf_typ_from_wf_env_typ.
rewrite_env (empty ++ E).
eapply wf_typ_strengthening; simpl_env; eauto.
Case "typing_app".
repeat split...
destruct IHtyping1 as [_ [_ K]].
inversion K...
Case "typing_tabs".
pick fresh Y.
destruct (H0 Y) as [Hok [J K]]...
inversion Hok; subst.
repeat split...
SCase "Second of original three conjuncts".
pick fresh X and apply expr_tabs.
eauto using type_from_wf_typ, wf_typ_from_wf_env_sub...
destruct (H0 X)...
SCase "Third of original three conjuncts".
pick fresh Z and apply wf_typ_all...
destruct (H0 Z)...
Case "typing_tapp".
destruct (sub_regular _ _ _ H0) as [R1 [R2 R3]].
repeat split...
SCase "Second of original three conjuncts".
apply expr_tapp...
eauto using type_from_wf_typ.
SCase "Third of original three conjuncts".
destruct IHtyping as [R1' [R2' R3']].
eapply wf_typ_open; eauto.
Case "typing_sub".
repeat split...
destruct (sub_regular _ _ _ H0)...
Case "typing_let".
repeat split...
SCase "Second of original three conjuncts".
pick fresh y and apply expr_let...
destruct (H1 y) as [K1 [K2 K3]]...
SCase "Third of original three conjuncts".
pick fresh y.
destruct (H1 y) as [K1 [K2 K3]]...
rewrite_env (empty ++ E).
eapply wf_typ_strengthening; simpl_env; eauto.
Case "typing_case".
repeat split...
SCase "Second of original three conjuncts".
pick fresh x and apply expr_case...
destruct (H1 x) as [? [? ?]]...
destruct (H3 x) as [? [? ?]]...
SCase "Third of original three conjuncts".
pick fresh y.
destruct (H1 y) as [K1 [K2 K3]]...
rewrite_env (empty ++ E).
eapply wf_typ_strengthening; simpl_env; eauto.
Qed.

Lemma value_regular : forall e,
value e ->
expr e.