X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fbasic_2%2Fsyntax%2Fvoids_length.ma;h=60d41924ba064ea6e45437c45da4cc49f4d42e84;hb=a4998de03fae0f36cde8abf17f45ea115845e849;hp=30738ee24709f3b42e7ddb6d41bf41de4c0b1e42;hpb=1ed30536a512158b064802524175996b01c3abdc;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/basic_2/syntax/voids_length.ma b/matita/matita/contribs/lambdadelta/basic_2/syntax/voids_length.ma
index 30738ee24..60d41924b 100644
--- a/matita/matita/contribs/lambdadelta/basic_2/syntax/voids_length.ma
+++ b/matita/matita/contribs/lambdadelta/basic_2/syntax/voids_length.ma
@@ -19,25 +19,40 @@ include "basic_2/syntax/voids.ma".
 
 (* Forward lemmas with length for local environments ************************)
 
+lemma voids_fwd_length_le_sn: ∀L1,L2,n1,n2. ⓧ*[n1]L1 ≋ ⓧ*[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 voids_fwd_length_le_dx: ∀L1,L2,n1,n2. ⓧ*[n1]L1 ≋ ⓧ*[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 voids_fwd_length: ∀L1,L2,n1,n2. ⓧ*[n1]L1 ≋ ⓧ*[n2]L2 →
                         |L1| + n2 = |L2| + n1.
-#L1 #L2 #n1 #n2 #H elim H -L1 -L2 -n1 -n2 normalize //
-#I1 #I2 #K1 #K2 #V #n #_ #IH 
-
-(* Main forward properties with length for local environments ***************)
-
-theorem voids_inj_length: ∀n1,n2,L1,L2. ⓧ*[n1]L1 = ⓧ*[n2]L2 →
-                          |L1| = |L2| → n1 = n2 ∧ L1 = L2.
-#n1 elim n1 -n1
-[ * /2 width=1 by conj/ #n2 #L1 #L2 | #n1 #IH * [ | #n2 ] #L1 #L2 ]
-[ <voids_zero #H destruct
-  <length_void <commutative_plus #H
-  elim (plus_xSy_x_false … H)
-| <voids_zero #H destruct
-  <length_void <commutative_plus #H
-  elim (plus_xSy_x_false … (sym_eq … H))
-| <voids_succ <voids_succ #H #HL12
-  elim (destruct_lbind_lbind_aux … H) -H (**) (* destruct lemma needed *)
-  #H #_ elim (IH … H HL12) -IH -H -HL12 /2 width=1 by conj/
-]
+#L1 #L2 #n1 #n2 #H elim H -L1 -L2 -n1 -n2 normalize
+/2 width=2 by injective_plus_r/
+qed-.
+
+lemma voids_fwd_length_minus: ∀L1,L2,n1,n2. ⓧ*[n1]L1 ≋ ⓧ*[n2]L2 →
+                              |L1| - n1 = |L2| - n2.
+/3 width=3 by voids_fwd_length, voids_fwd_length_le_dx, voids_fwd_length_le_sn, plus_to_minus_2/ qed-.
+
+lemma voids_inj_length: ∀L1,L2,n1,n2. ⓧ*[n1]L1 ≋ ⓧ*[n2]L2 →
+                        |L1| = |L2| → n1 = n2.
+#L1 #L2 #n1 #n2 #H #HL12
+lapply (voids_fwd_length … H) -H #H
+/2 width=2 by injective_plus_l/
+qed-.
+
+(* Inversion lemmas with length for local environments **********************)
+
+lemma voids_inv_void_dx_length: ∀L1,L2,n1,n2. ⓧ*[n1]L1 ≋ ⓧ*[n2]L2.ⓧ → |L1| ≤ |L2| →
+                                ∃∃m2. ⓧ*[n1]L1 ≋ ⓧ*[m2]L2 & n2 = ⫯m2 & n1 ≤ m2.
+#L1 #L2 #n1 #n2 #H #HL12
+lapply (voids_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 voids_inv_void_dx, ex3_intro/
 qed-.