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diff --git a/matita/matita/contribs/lambdadelta/basic_2/etc_new/lenv/lenv_append.ma b/matita/matita/contribs/lambdadelta/basic_2/etc_new/lenv/lenv_append.ma
new file mode 100644
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+++ b/matita/matita/contribs/lambdadelta/basic_2/etc_new/lenv/lenv_append.ma
@@ -0,0 +1,145 @@
+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||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 "ground_2/notation/functions/append_2.ma".
+include "ground_2/ynat/ynat_plus.ma".
+include "basic_2/notation/functions/snbind2_3.ma".
+include "basic_2/notation/functions/snabbr_2.ma".
+include "basic_2/notation/functions/snabst_2.ma".
+include "basic_2/grammar/lenv_length.ma".
+
+(* LOCAL ENVIRONMENTS *******************************************************)
+
+let rec append L K on K ≝ match K with
+[ LAtom       ⇒ L
+| LPair K I V ⇒ (append L K). ⓑ{I} V
+].
+
+interpretation "append (local environment)" 'Append L1 L2 = (append L1 L2).
+
+interpretation "local environment tail binding construction (binary)"
+   'SnBind2 I T L = (append (LPair LAtom I T) L).
+
+interpretation "tail abbreviation (local environment)"
+   'SnAbbr T L = (append (LPair LAtom Abbr T) L).
+
+interpretation "tail abstraction (local environment)"
+   'SnAbst L T = (append (LPair LAtom Abst T) L).
+
+definition d_appendable_sn: predicate (lenv→relation term) ≝ λR.
+                            ∀K,T1,T2. R K T1 T2 → ∀L. R (L @@ K) T1 T2.
+
+(* Basic properties *********************************************************)
+
+lemma append_atom: ∀L. L @@ ⋆ = L.
+// qed.
+
+lemma append_pair: ∀I,L,K,V. L @@ (K.ⓑ{I}V) = (L @@ K).ⓑ{I}V.
+// qed.
+
+lemma append_atom_sn: ∀L. ⋆ @@ L = L.
+#L elim L -L //
+#L #I #V >append_pair //
+qed.
+
+lemma append_assoc: associative … append.
+#L1 #L2 #L3 elim L3 -L3 //
+qed.
+
+lemma append_length: ∀L1,L2. |L1 @@ L2| = |L1| + |L2|.
+#L1 #L2 elim L2 -L2 //
+#L2 #I #V2 >append_pair >length_pair >length_pair //
+qed.
+
+lemma ltail_length: ∀I,L,V. |ⓑ{I}V.L| = ⫯|L|.
+#I #L #V >append_length //
+qed.
+
+(* Basic_1: was just: chead_ctail *)
+lemma lpair_ltail: ∀L,I,V. ∃∃J,K,W. L.ⓑ{I}V = ⓑ{J}W.K & |L| = |K|.
+#L elim L -L /2 width=5 by ex2_3_intro/
+#L #Z #X #IHL #I #V elim (IHL Z X) -IHL
+#J #K #W #H #_ >H -H >ltail_length
+@(ex2_3_intro … J (K.ⓑ{I}V) W) //
+qed-.
+
+(* Basic inversion lemmas ***************************************************)
+
+lemma append_inj_sn: ∀K1,K2,L1,L2. L1 @@ K1 = L2 @@ K2 → |K1| = |K2| →
+                     L1 = L2 ∧ K1 = K2.
+#K1 elim K1 -K1
+[ * /2 width=1 by conj/
+  #K2 #I2 #V2 #L1 #L2 #_ >length_atom >length_pair
+  #H elim (ysucc_inv_O_sn … H)
+| #K1 #I1 #V1 #IH *
+  [ #L1 #L2 #_ >length_atom >length_pair
+    #H elim (ysucc_inv_O_dx … H)
+  | #K2 #I2 #V2 #L1 #L2 #H1 #H2
+    elim (destruct_lpair_lpair_aux … H1) -H1 #H1 #H3 #H4 destruct (**) (* destruct lemma needed *)
+    elim (IH … H1) -IH -H1 /3 width=1 by ysucc_inv_inj, conj/
+  ]
+]
+qed-.
+
+(* Note: lemma 750 *)
+lemma append_inj_dx: ∀K1,K2,L1,L2. L1 @@ K1 = L2 @@ K2 → |L1| = |L2| →
+                     L1 = L2 ∧ K1 = K2.
+#K1 elim K1 -K1
+[ * /2 width=1 by conj/
+  #K2 #I2 #V2 #L1 #L2 >append_atom >append_pair #H destruct
+  >length_pair >append_length <yplus_succ2 #H
+  elim (discr_yplus_xy_x … H) -H #H
+  [ elim (ylt_yle_false (|L2|) (∞)) // | elim (ysucc_inv_O_dx … H) ]
+| #K1 #I1 #V1 #IH *
+  [ #L1 #L2 >append_pair >append_atom #H destruct
+    >length_pair >append_length <yplus_succ2 #H
+    elim (discr_yplus_x_xy … H) -H #H
+    [ elim (ylt_yle_false (|L1|) (∞)) // | elim (ysucc_inv_O_dx … H) ]
+  | #K2 #I2 #V2 #L1 #L2 >append_pair >append_pair #H1 #H2
+    elim (destruct_lpair_lpair_aux … H1) -H1 #H1 #H3 #H4 destruct (**) (* destruct lemma needed *)
+    elim (IH … H1) -IH -H1 /2 width=1 by conj/
+  ]
+]
+qed-.
+
+lemma append_inv_refl_dx: ∀L,K. L @@ K = L → K = ⋆.
+#L #K #H elim (append_inj_dx … (⋆) … H) //
+qed-.
+
+lemma append_inv_pair_dx: ∀I,L,K,V. L @@ K = L.ⓑ{I}V → K = ⋆.ⓑ{I}V.
+#I #L #K #V #H elim (append_inj_dx … (⋆.ⓑ{I}V) … H) //
+qed-.
+
+lemma length_inv_pos_dx_ltail: ∀L,l. |L| = ⫯l →
+                               ∃∃I,K,V. |K| = l & L = ⓑ{I}V.K.
+#Y #l #H elim (length_inv_pos_dx … H) -H #I #L #V #Hl #HLK destruct
+elim (lpair_ltail L I V) /2 width=5 by ex2_3_intro/
+qed-.
+
+lemma length_inv_pos_sn_ltail: ∀L,l. ⫯l = |L| →
+                               ∃∃I,K,V. l = |K| & L = ⓑ{I}V.K.
+#Y #l #H elim (length_inv_pos_sn … H) -H #I #L #V #Hl #HLK destruct
+elim (lpair_ltail L I V) /2 width=5 by ex2_3_intro/
+qed-.
+
+(* Basic eliminators ********************************************************)
+
+(* Basic_1: was: c_tail_ind *)
+lemma lenv_ind_alt: ∀R:predicate lenv.
+                    R (⋆) → (∀I,L,T. R L → R (ⓑ{I}T.L)) →
+                    ∀L. R L.
+#R #IH1 #IH2 #L @(ynat_f_ind … length … L) -L #x #IHx * // -IH1
+#L #I #V #H destruct elim (lpair_ltail L I V)
+/4 width=1 by monotonic_ylt_plus_sn/
+qed-.