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diff --git a/matita/matita/contribs/lambdadelta/basic_2/syntax/lveq_length.ma b/matita/matita/contribs/lambdadelta/basic_2/syntax/lveq_length.ma
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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/syntax/lenv_length.ma".
+include "basic_2/syntax/lveq.ma".
+
+(* EQUIVALENCE FOR LOCAL ENVIRONMENTS UP TO EXCLUSION BINDERS ***************)
+
+lemma lveq_eq_ex: ∀L1,L2. |L1| = |L2| → ∃n. L1 ≋ⓧ*[n, n] L2.
+#L1 elim L1 -L1
+[ #Y2 #H >(length_inv_zero_sn … H) -Y2 /2 width=3 by lveq_atom, ex_intro/
+| #K1 * [ * | #I1 #V1 ] #IH #Y2 #H
+  elim (length_inv_succ_sn … H) -H * [1,3: * |*: #I2 #V2 ] #K2 #HK #H destruct 
+  elim (IH … HK) -IH -HK #n #HK
+  /4 width=3 by lveq_pair_sn, lveq_pair_dx, lveq_void_sn, lveq_void_dx, ex_intro/
+]
+qed-.
+
+(* Forward lemmas with length for local environments ************************)
+
+lemma lveq_fwd_length_le_sn: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 → n1 ≤ |L1|.
+#L1 #L2 #n1 #n2 #H elim H -L1 -L2 -n1 -n2 normalize
+/2 width=1 by le_S_S/
+qed-.
+
+lemma lveq_fwd_length_le_dx: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 → n2 ≤ |L2|.
+#L1 #L2 #n1 #n2 #H elim H -L1 -L2 -n1 -n2 normalize
+/2 width=1 by le_S_S/
+qed-.
+
+lemma lveq_fwd_length: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 →
+                       |L1| + n2 = |L2| + n1.
+#L1 #L2 #n1 #n2 #H elim H -L1 -L2 -n1 -n2 normalize
+/2 width=2 by injective_plus_r/
+qed-.
+
+lemma lveq_fwd_length_eq: ∀L1,L2,n. L1 ≋ⓧ*[n, n] L2 → |L1| = |L2|.
+/3 width=2 by lveq_fwd_length, injective_plus_l/ qed-.
+
+lemma lveq_fwd_length_minus: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 →
+                             |L1| - n1 = |L2| - n2.
+/3 width=3 by lveq_fwd_length, lveq_fwd_length_le_dx, lveq_fwd_length_le_sn, plus_to_minus_2/ qed-.
+
+lemma lveq_inj_length: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 →
+                       |L1| = |L2| → n1 = n2.
+#L1 #L2 #n1 #n2 #H #HL12
+lapply (lveq_fwd_length … H) -H #H
+/2 width=2 by injective_plus_l/
+qed-.
+(*
+(* Inversion lemmas with length for local environments **********************)
+                   
+lemma lveq_inv_void_dx_length: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2.ⓧ → |L1| ≤ |L2| →
+                               ∃∃m2. L1 ≋ ⓧ*[n1, m2] L2 & n2 = ⫯m2 & n1 ≤ m2.
+#L1 #L2 #n1 #n2 #H #HL12
+lapply (lveq_fwd_length … H) normalize >plus_n_Sm #H0
+lapply (plus2_inv_le_sn … H0 HL12) -H0 -HL12 #H0
+elim (le_inv_S1 … H0) -H0 #m2 #Hm2 #H0 destruct
+/3 width=4 by lveq_inv_void_dx, ex3_intro/
+qed-.
+*)
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