/2 width=3/ qed.
(* Basic_1: was by definition: pr0_refl *)
-lemma tpr_refl: ∀T. T ➡ T.
+lemma tpr_refl: reflexive … tpr.
#T elim T -T //
#I elim I -I /2 width=1/
qed.
| ∃∃V,T. T ➡ #i & T1 = ⓝV. T.
/2 width=3/ qed-.
+(* Basic forward lemmas *****************************************************)
+
+lemma tpr_fwd_shift1: ∀L1,T1,T. L1 @@ T1 ➡ T →
+ ∃∃L2,T2. |L1| = |L2| & T = L2 @@ T2.
+#L1 @(lenv_ind_dx … L1) -L1 normalize
+[ #T1 #T #HT1
+ @(ex2_2_intro … (⋆)) // (**) (* explicit constructor *)
+| #I #L1 #V1 #IH #T1 #X
+ >shift_append_assoc normalize #H
+ elim (tpr_inv_bind1 … H) -H *
+ [ #V0 #T0 #X0 #_ #HT10 #H0 #H destruct
+ elim (IH … HT10) -IH -T1 #L #T #HL1 #H destruct
+ elim (tps_fwd_shift1 … H0) -T #L2 #T2 #HL2 #H destruct
+ >append_length >HL1 >HL2 -L1 -L
+ @(ex2_2_intro … (⋆.ⓑ{I}V0@@L2) T2) [ >append_length ] // /2 width=3/ (**) (* explicit constructor *)
+ | #T #_ #_ #H destruct
+ ]
+]
+qed-.
+
(* Basic_1: removed theorems 3:
pr0_subst0_back pr0_subst0_fwd pr0_subst0
Basic_1: removed local theorems: 1: pr0_delta_tau