+lemma subst_inv_bind1_aux: ∀d,e,L,U1,U2. L ⊢ ↓[d, e] U1 ≡ U2 →
+ ∀I,V1,T1. U1 = 𝕓{I} V1. T1 →
+ ∃∃V2,T2. subst L V1 d e V2 &
+ subst (L. 𝕓{I} V1) T1 (d + 1) e T2 &
+ U2 = 𝕓{I} V2. T2.
+#d #e #L #U1 #U2 #H elim H -H d e L U1 U2
+[ #L #k #d #e #I #V1 #T1 #H destruct
+| #L #i #d #e #_ #I #V1 #T1 #H destruct
+| #L #K #V #U1 #U2 #i #d #e #_ #_ #_ #_ #_ #_ #I #V1 #T1 #H destruct
+| #L #i #d #e #_ #I #V1 #T1 #H destruct
+| #L #J #V1 #V2 #T1 #T2 #d #e #HV12 #HT12 #_ #_ #I #V #T #H destruct /2 width=5/
+| #L #J #V1 #V2 #T1 #T2 #d #e #_ #_ #_ #_ #I #V #T #H destruct
+]
+qed.
+
+lemma subst_inv_bind1: ∀d,e,L,I,V1,T1,U2. L ⊢ ↓[d, e] 𝕓{I} V1. T1 ≡ U2 →
+ ∃∃V2,T2. subst L V1 d e V2 &
+ subst (L. 𝕓{I} V1) T1 (d + 1) e T2 &
+ U2 = 𝕓{I} V2. T2.
+/2/ qed.
+
+lemma subst_inv_flat1_aux: ∀d,e,L,U1,U2. L ⊢ ↓[d, e] U1 ≡ U2 →
+ ∀I,V1,T1. U1 = 𝕗{I} V1. T1 →
+ ∃∃V2,T2. subst L V1 d e V2 & subst L T1 d e T2 &
+ U2 = 𝕗{I} V2. T2.
+#d #e #L #U1 #U2 #H elim H -H d e L U1 U2
+[ #L #k #d #e #I #V1 #T1 #H destruct
+| #L #i #d #e #_ #I #V1 #T1 #H destruct
+| #L #K #V #U1 #U2 #i #d #e #_ #_ #_ #_ #_ #_ #I #V1 #T1 #H destruct
+| #L #i #d #e #_ #I #V1 #T1 #H destruct
+| #L #J #V1 #V2 #T1 #T2 #d #e #_ #_ #_ #_ #I #V #T #H destruct
+| #L #J #V1 #V2 #T1 #T2 #d #e #HV12 #HT12 #_ #_ #I #V #T #H destruct /2 width=5/
+]
+qed.
+
+lemma subst_inv_flat1: ∀d,e,L,I,V1,T1,U2. L ⊢ ↓[d, e] 𝕗{I} V1. T1 ≡ U2 →
+ ∃∃V2,T2. subst L V1 d e V2 & subst L T1 d e T2 &
+ U2 = 𝕗{I} V2. T2.
+/2/ qed.
+(*