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+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||         The HELM team.                                      *)
+(*      ||A||         http://helm.cs.unibo.it                             *)
+(*      \   /                                                             *)
+(*       \ /        This file is distributed under the terms of the       *)
+(*        v         GNU General Public License Version 2                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+include "basic_2/substitution/cpys_lift.ma".
+include "basic_2/substitution/cofrees.ma".
+
+(* CONTEXT-SENSITIVE EXCLUSION FROM FREE VARIABLES **************************)
+
+(* Advanced properties ******************************************************)
+
+lemma cofrees_lref_skip: ∀L,d,i,j. j < i → yinj j < d → L ⊢ i ~ϵ 𝐅*[d]⦃#j⦄.
+#L #d #i #j #Hji #Hjd #X #H elim (cpys_inv_lref1_Y2 … H) -H
+[ #H destruct /3 width=2 by lift_lref_lt, ex_intro/
+| * #I #K #W1 #W2 #Hdj elim (ylt_yle_false … Hdj) -i -I -L -K -W1 -W2 -X //
+]
+qed.
+
+lemma cofrees_lref_lt: ∀L,d,i,j. i < j → L ⊢ i ~ϵ 𝐅*[d]⦃#j⦄.
+#L #d #i #j #Hij #X #H elim (cpys_inv_lref1_Y2 … H) -H
+[ #H destruct /3 width=2 by lift_lref_ge_minus, ex_intro/
+| * #I #K #V1 #V2 #_ #_ #_ #H -I -L -K -V1 -d
+  elim (lift_split … H i j) /2 width=2 by lt_to_le, ex_intro/
+]
+qed.
+
+lemma cofrees_lref_gt: ∀I,L,K,W,d,i,j. j < i → ⇩[j] L ≡ K.ⓑ{I}W → 
+                       K ⊢ (i-j-1) ~ϵ 𝐅*[O]⦃W⦄ → L ⊢ i ~ϵ 𝐅*[d]⦃#j⦄.
+#I #L #K #W1 #d #i #j #Hji #HLK #HW1 #X #H elim (cpys_inv_lref1_Y2 … H) -H
+[ #H destruct /3 width=2 by lift_lref_lt, ex_intro/
+| * #I0 #K0 #W0 #W2 #Hdj #HLK0 #HW12 #HW2 lapply (ldrop_mono … HLK0 … HLK) -L
+  #H destruct elim (HW1 … HW12) -I -K -W1 -d
+  #V2 #HVW2 elim (lift_trans_le … HVW2 … HW2) -W2 //
+  >minus_plus <plus_minus_m_m /2 width=2 by ex_intro/
+]
+qed.
+
+lemma cofrees_lref_free: ∀L,d,i,j. |L| ≤ j → j < i → L ⊢ i ~ϵ 𝐅*[d]⦃#j⦄.
+#L #d #i #j #Hj #Hji #X #H elim (cpys_inv_lref1_Y2 … H) -H
+[ #H destruct /3 width=2 by lift_lref_lt, ex_intro/
+| * #I #K #W1 #W2 #_ #HLK lapply (ldrop_fwd_length_lt2 … HLK) -I
+  #H elim (lt_refl_false j) -d -i -K -W1 -W2 -X /2 width=3 by lt_to_le_to_lt/
+]
+qed.
+
+(* Advanced negated inversion lemmas ****************************************)
+
+lemma frees_inv_lref_gt: ∀L,d,i,j. j < i → (L ⊢ i ~ϵ 𝐅*[d]⦃#j⦄ → ⊥) →
+                         ∃∃I,K,W. ⇩[j] L ≡ K.ⓑ{I}W & (K ⊢ (i-j-1) ~ϵ 𝐅*[0]⦃W⦄ → ⊥) & d ≤ yinj j.
+#L #d #i #j #Hji #H elim (ylt_split j d) #Hjd
+[ elim H -H /2 width=6 by cofrees_lref_skip/ 
+| elim (lt_or_ge j (|L|)) #Hj
+  [ elim (ldrop_O1_lt … Hj) -Hj /4 width=10 by cofrees_lref_gt, ex3_3_intro/
+  | elim H -H /2 width=6 by cofrees_lref_free/
+  ]
+]
+qed-.
+
+lemma frees_inv_lref_free: ∀L,d,i,j. (L ⊢ i ~ϵ 𝐅*[d]⦃#j⦄  → ⊥) → |L| ≤ j → j = i.
+#L #d #i #j #H #Hj elim (lt_or_eq_or_gt i j) //
+#Hij elim H -H /2 width=6 by cofrees_lref_lt, cofrees_lref_free/
+qed-.
+
+lemma frees_inv_gen: ∀L,U,d,i. (L ⊢ i ~ϵ 𝐅*[d]⦃U⦄ → ⊥) →
+                     ∃∃U0.  ⦃⋆, L⦄ ⊢ U ▶*[d, ∞] U0 & (∀T. ⇧[i, 1] T ≡ U0 → ⊥).
+#L #U @(f2_ind … rfw … L U) -L -U
+#n #IH #L * *
+[ -IH #k #_ #d #i #H elim H -H //
+| #j #Hn #d #i #H elim (lt_or_eq_or_gt i j)
+  [ -n #Hij elim H -H /2 width=5 by cofrees_lref_lt/
+  | -H -n #H destruct /3 width=7 by lift_inv_lref2_be, ex2_intro/
+  | #Hji elim (frees_inv_lref_gt … H) // -H
+    #I #K #W1 #HLK #H #Hdj elim (IH … H) /2 width=2 by ldrop_fwd_rfw/ -H -n
+    #W2 #HW12 #HnW2 elim (lift_total W2 0 (j+1))
+    #U2 #HWU2 @(ex2_intro … U2) /2 width=7 by cpys_subst_Y2/ -I -L -K -W1 -d
+    #T2 #HTU2 elim (lift_div_le … HWU2 (i-j-1) 1 T2) /2 width=2 by/ -W2
+    >minus_plus <plus_minus_m_m //
+  ]
+| -IH #p #_ #d #i #H elim H -H //
+| #a #I #W #U #Hn #d #i #H elim (frees_inv_bind … H) -H
+  #H elim (IH … H) // -H -n
+  /4 width=9 by cpys_bind, nlift_bind_dx, nlift_bind_sn, ex2_intro/
+| #I #W #U #Hn #d #i #H elim (frees_inv_flat … H) -H
+  #H elim (IH … H) // -H -n
+  /4 width=9 by cpys_flat, nlift_flat_dx, nlift_flat_sn, ex2_intro/
+]
+qed-.