X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;ds=sidebyside;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fbasic_2%2Frelocation%2Fldrop.ma;h=94c6b0f733c2a3037932f8fdfd2c3acc6de847a7;hb=82fe07c3accb68ca4f7a1870a046128fe980dced;hp=6d91d0aa0af38f4d4bf16ba424fc05bb613edb90;hpb=f16bbb93ecb40fa40f736e0b1158e1c7676a640a;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/basic_2/relocation/ldrop.ma b/matita/matita/contribs/lambdadelta/basic_2/relocation/ldrop.ma
index 6d91d0aa0..94c6b0f73 100644
--- a/matita/matita/contribs/lambdadelta/basic_2/relocation/ldrop.ma
+++ b/matita/matita/contribs/lambdadelta/basic_2/relocation/ldrop.ma
@@ -12,15 +12,17 @@
 (*                                                                        *)
 (**************************************************************************)
 
-include "basic_2/grammar/cl_weight.ma".
+include "ground_2/lstar.ma".
+include "basic_2/notation/relations/rdrop_4.ma".
+include "basic_2/grammar/lenv_length.ma".
+include "basic_2/grammar/lenv_weight.ma".
 include "basic_2/relocation/lift.ma".
-include "basic_2/relocation/lsubr.ma".
 
 (* LOCAL ENVIRONMENT SLICING ************************************************)
 
 (* Basic_1: includes: drop_skip_bind *)
-inductive ldrop: nat → nat → relation lenv ≝
-| ldrop_atom : ∀d,e. ldrop d e (⋆) (⋆)
+inductive ldrop: relation4 nat nat lenv lenv ≝
+| ldrop_atom : ∀d. ldrop d 0 (⋆) (⋆)
 | ldrop_pair : ∀L,I,V. ldrop 0 0 (L. ⓑ{I} V) (L. ⓑ{I} V)
 | ldrop_ldrop: ∀L1,L2,I,V,e. ldrop 0 e L1 L2 → ldrop 0 (e + 1) (L1. ⓑ{I} V) L2
 | ldrop_skip : ∀L1,L2,I,V1,V2,d,e.
@@ -30,76 +32,63 @@ inductive ldrop: nat → nat → relation lenv ≝
 
 interpretation "local slicing" 'RDrop d e L1 L2 = (ldrop d e L1 L2).
 
-definition l_liftable: (lenv → relation term) → Prop ≝
+definition l_liftable: predicate (lenv → relation term) ≝
                        λR. ∀K,T1,T2. R K T1 T2 → ∀L,d,e. ⇩[d, e] L ≡ K →
                        ∀U1. ⇧[d, e] T1 ≡ U1 → ∀U2. ⇧[d, e] T2 ≡ U2 → R L U1 U2.
 
-definition l_deliftable_sn: (lenv → relation term) → Prop ≝
+definition l_deliftable_sn: predicate (lenv → relation term) ≝
                             λR. ∀L,U1,U2. R L U1 U2 → ∀K,d,e. ⇩[d, e] L ≡ K →
                             ∀T1. ⇧[d, e] T1 ≡ U1 →
                             ∃∃T2. ⇧[d, e] T2 ≡ U2 & R K T1 T2.
 
-definition dropable_sn: relation lenv → Prop ≝
+definition dropable_sn: predicate (relation lenv) ≝
                         λR. ∀L1,K1,d,e. ⇩[d, e] L1 ≡ K1 → ∀L2. R L1 L2 →
                         ∃∃K2. R K1 K2 & ⇩[d, e] L2 ≡ K2.
 
-definition dedropable_sn: relation lenv → Prop ≝
+definition dedropable_sn: predicate (relation lenv) ≝
                           λR. ∀L1,K1,d,e. ⇩[d, e] L1 ≡ K1 → ∀K2. R K1 K2 →
                           ∃∃L2. R L1 L2 & ⇩[d, e] L2 ≡ K2.
 
-definition dropable_dx: relation lenv → Prop ≝
+definition dropable_dx: predicate (relation lenv) ≝
                         λR. ∀L1,L2. R L1 L2 → ∀K2,e. ⇩[0, e] L2 ≡ K2 →
                         ∃∃K1. ⇩[0, e] L1 ≡ K1 & R K1 K2.
 
 (* Basic inversion lemmas ***************************************************)
 
-fact ldrop_inv_refl_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → d = 0 → e = 0 → L1 = L2.
-#d #e #L1 #L2 * -d -e -L1 -L2
-[ //
-| //
-| #L1 #L2 #I #V #e #_ #_ >commutative_plus normalize #H destruct
-| #L1 #L2 #I #V1 #V2 #d #e #_ #_ >commutative_plus normalize #H destruct
-]
-qed.
-
-(* Basic_1: was: drop_gen_refl *)
-lemma ldrop_inv_refl: ∀L1,L2. ⇩[0, 0] L1 ≡ L2 → L1 = L2.
-/2 width=5/ qed-.
-
 fact ldrop_inv_atom1_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → L1 = ⋆ →
-                          L2 = ⋆.
+                          L2 = ⋆ ∧ e = 0.
 #d #e #L1 #L2 * -d -e -L1 -L2
-[ //
+[ /2 width=1/
 | #L #I #V #H destruct
 | #L1 #L2 #I #V #e #_ #H destruct
 | #L1 #L2 #I #V1 #V2 #d #e #_ #_ #H destruct
 ]
-qed.
+qed-.
 
 (* Basic_1: was: drop_gen_sort *)
-lemma ldrop_inv_atom1: ∀d,e,L2. ⇩[d, e] ⋆ ≡ L2 → L2 = ⋆.
-/2 width=5/ qed-.
+lemma ldrop_inv_atom1: ∀d,e,L2. ⇩[d, e] ⋆ ≡ L2 → L2 = ⋆ ∧ e = 0.
+/2 width=4 by ldrop_inv_atom1_aux/ qed-.
 
-fact ldrop_inv_O1_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → d = 0 →
-                       ∀K,I,V. L1 = K. ⓑ{I} V →
-                       (e = 0 ∧ L2 = K. ⓑ{I} V) ∨
-                       (0 < e ∧ ⇩[d, e - 1] K ≡ L2).
+fact ldrop_inv_O1_pair1_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → d = 0 →
+                             ∀K,I,V. L1 = K. ⓑ{I} V →
+                             (e = 0 ∧ L2 = K. ⓑ{I} V) ∨
+                             (0 < e ∧ ⇩[d, e - 1] K ≡ L2).
 #d #e #L1 #L2 * -d -e -L1 -L2
-[ #d #e #_ #K #I #V #H destruct
+[ #d #_ #K #I #V #H destruct
 | #L #I #V #_ #K #J #W #HX destruct /3 width=1/
 | #L1 #L2 #I #V #e #HL12 #_ #K #J #W #H destruct /3 width=1/
 | #L1 #L2 #I #V1 #V2 #d #e #_ #_ >commutative_plus normalize #H destruct
 ]
-qed.
+qed-.
 
-lemma ldrop_inv_O1: ∀e,K,I,V,L2. ⇩[0, e] K. ⓑ{I} V ≡ L2 →
-                    (e = 0 ∧ L2 = K. ⓑ{I} V) ∨
-                    (0 < e ∧ ⇩[0, e - 1] K ≡ L2).
-/2 width=3/ qed-.
+lemma ldrop_inv_O1_pair1: ∀e,K,I,V,L2. ⇩[0, e] K. ⓑ{I} V ≡ L2 →
+                          (e = 0 ∧ L2 = K. ⓑ{I} V) ∨
+                          (0 < e ∧ ⇩[0, e - 1] K ≡ L2).
+/2 width=3 by ldrop_inv_O1_pair1_aux/ qed-.
 
 lemma ldrop_inv_pair1: ∀K,I,V,L2. ⇩[0, 0] K. ⓑ{I} V ≡ L2 → L2 = K. ⓑ{I} V.
 #K #I #V #L2 #H
-elim (ldrop_inv_O1 … H) -H * // #H destruct
+elim (ldrop_inv_O1_pair1 … H) -H * // #H destruct
 elim (lt_refl_false … H)
 qed-.
 
@@ -107,7 +96,7 @@ qed-.
 lemma ldrop_inv_ldrop1: ∀e,K,I,V,L2.
                         ⇩[0, e] K. ⓑ{I} V ≡ L2 → 0 < e → ⇩[0, e - 1] K ≡ L2.
 #e #K #I #V #L2 #H #He
-elim (ldrop_inv_O1 … H) -H * // #H destruct
+elim (ldrop_inv_O1_pair1 … H) -H * // #H destruct
 elim (lt_refl_false … He)
 qed-.
 
@@ -117,27 +106,27 @@ fact ldrop_inv_skip1_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → 0 < d →
                                    ⇧[d - 1, e] V2 ≡ V1 &
                                    L2 = K2. ⓑ{I} V2.
 #d #e #L1 #L2 * -d -e -L1 -L2
-[ #d #e #_ #I #K #V #H destruct
+[ #d #_ #I #K #V #H destruct
 | #L #I #V #H elim (lt_refl_false … H)
 | #L1 #L2 #I #V #e #_ #H elim (lt_refl_false … H)
 | #X #L2 #Y #Z #V2 #d #e #HL12 #HV12 #_ #I #L1 #V1 #H destruct /2 width=5/
 ]
-qed.
+qed-.
 
 (* Basic_1: was: drop_gen_skip_l *)
 lemma ldrop_inv_skip1: ∀d,e,I,K1,V1,L2. ⇩[d, e] K1. ⓑ{I} V1 ≡ L2 → 0 < d →
                        ∃∃K2,V2. ⇩[d - 1, e] K1 ≡ K2 &
                                 ⇧[d - 1, e] V2 ≡ V1 &
                                 L2 = K2. ⓑ{I} V2.
-/2 width=3/ qed-.
+/2 width=3 by ldrop_inv_skip1_aux/ qed-.
 
 lemma ldrop_inv_O1_pair2: ∀I,K,V,e,L1. ⇩[0, e] L1 ≡ K. ⓑ{I} V →
                           (e = 0 ∧ L1 = K. ⓑ{I} V) ∨
                           ∃∃I1,K1,V1. ⇩[0, e - 1] K1 ≡ K. ⓑ{I} V & L1 = K1.ⓑ{I1}V1 & 0 < e.
 #I #K #V #e *
-[ #H lapply (ldrop_inv_atom1 … H) -H #H destruct
+[ #H elim (ldrop_inv_atom1 … H) -H #H destruct
 | #L1 #I1 #V1 #H
-  elim (ldrop_inv_O1 … H) -H *
+  elim (ldrop_inv_O1_pair1 … H) -H *
   [ #H1 #H2 destruct /3 width=1/
   | /3 width=5/
   ]
@@ -150,24 +139,25 @@ fact ldrop_inv_skip2_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → 0 < d →
                                    ⇧[d - 1, e] V2 ≡ V1 &
                                    L1 = K1. ⓑ{I} V1.
 #d #e #L1 #L2 * -d -e -L1 -L2
-[ #d #e #_ #I #K #V #H destruct
+[ #d #_ #I #K #V #H destruct
 | #L #I #V #H elim (lt_refl_false … H)
 | #L1 #L2 #I #V #e #_ #H elim (lt_refl_false … H)
 | #L1 #X #Y #V1 #Z #d #e #HL12 #HV12 #_ #I #L2 #V2 #H destruct /2 width=5/
 ]
-qed.
+qed-.
 
 (* Basic_1: was: drop_gen_skip_r *)
 lemma ldrop_inv_skip2: ∀d,e,I,L1,K2,V2. ⇩[d, e] L1 ≡ K2. ⓑ{I} V2 → 0 < d →
                        ∃∃K1,V1. ⇩[d - 1, e] K1 ≡ K2 & ⇧[d - 1, e] V2 ≡ V1 &
                                 L1 = K1. ⓑ{I} V1.
-/2 width=3/ qed-.
+/2 width=3 by ldrop_inv_skip2_aux/ qed-.
 
 (* Basic properties *********************************************************)
 
 (* Basic_1: was by definition: drop_refl *)
-lemma ldrop_refl: ∀L. ⇩[0, 0] L ≡ L.
+lemma ldrop_refl: ∀L,d. ⇩[d, 0] L ≡ L.
 #L elim L -L //
+#L #I #V #IHL #d @(nat_ind_plus … d) -d // /2 width=1/
 qed.
 
 lemma ldrop_ldrop_lt: ∀L1,L2,I,V,e.
@@ -181,50 +171,39 @@ lemma ldrop_skip_lt: ∀L1,L2,I,V1,V2,d,e.
 #L1 #L2 #I #V1 #V2 #d #e #HL12 #HV21 #Hd >(plus_minus_m_m d 1) // /2 width=1/
 qed.
 
-lemma ldrop_O1_le: ∀i,L. i ≤ |L| → ∃K. ⇩[0, i] L ≡ K.
-#i @(nat_ind_plus … i) -i /2 width=2/
-#i #IHi *
+lemma ldrop_O1_le: ∀e,L. e ≤ |L| → ∃K. ⇩[0, e] L ≡ K.
+#e @(nat_ind_plus … e) -e /2 width=2/
+#e #IHe *
 [ #H lapply (le_n_O_to_eq … H) -H >commutative_plus normalize #H destruct
 | #L #I #V normalize #H
-  elim (IHi L ?) -IHi /2 width=1/ -H /3 width=2/
+  elim (IHe L) -IHe /2 width=1/ -H /3 width=2/
 ]
 qed.
 
-lemma ldrop_O1_lt: ∀L,i. i < |L| → ∃∃I,K,V. ⇩[0, i] L ≡ K.ⓑ{I}V.
+lemma ldrop_O1_lt: ∀L,e. e < |L| → ∃∃I,K,V. ⇩[0, e] L ≡ K.ⓑ{I}V.
 #L elim L -L
-[ #i #H elim (lt_zero_false … H)
-| #L #I #V #IHL #i @(nat_ind_plus … i) -i /2 width=4/
-  #i #_ normalize #H
-  elim (IHL i ? ) -IHL /2 width=1/ -H /3 width=4/
+[ #e #H elim (lt_zero_false … H)
+| #L #I #V #IHL #e @(nat_ind_plus … e) -e /2 width=4/
+  #e #_ normalize #H
+  elim (IHL e) -IHL /2 width=1/ -H /3 width=4/
 ]
 qed.
 
-lemma ldrop_lsubr_ldrop2_abbr: ∀L1,L2,d,e. L1 ⊑ [d, e] L2 →
-                               ∀K2,V,i. ⇩[0, i] L2 ≡ K2. ⓓV →
-                               d ≤ i → i < d + e →
-                               ∃∃K1. K1 ⊑ [0, d + e - i - 1] K2 &
-                                     ⇩[0, i] L1 ≡ K1. ⓓV.
-#L1 #L2 #d #e #H elim H -L1 -L2 -d -e
-[ #d #e #K1 #V #i #H
-  lapply (ldrop_inv_atom1 … H) -H #H destruct
-| #L1 #L2 #K1 #V #i #_ #_ #H
-  elim (lt_zero_false … H)
-| #L1 #L2 #V #e #HL12 #IHL12 #K1 #W #i #H #_ #Hie
-  elim (ldrop_inv_O1 … H) -H * #Hi #HLK1
-  [ -IHL12 -Hie destruct
-    <minus_n_O <minus_plus_m_m // /2 width=3/
-  | -HL12
-    elim (IHL12 … HLK1 ? ?) -IHL12 -HLK1 // /2 width=1/ -Hie >minus_minus_comm >arith_b1 // /4 width=3/
-  ]
-| #L1 #L2 #I #V1 #V2 #e #_ #IHL12 #K1 #W #i #H #_ #Hie
-  elim (ldrop_inv_O1 … H) -H * #Hi #HLK1
-  [ -IHL12 -Hie -Hi destruct
-  | elim (IHL12 … HLK1 ? ?) -IHL12 -HLK1 // /2 width=1/ -Hie >minus_minus_comm >arith_b1 // /3 width=3/
-  ]
-| #L1 #L2 #I1 #I2 #V1 #V2 #d #e #_ #IHL12 #K1 #V #i #H #Hdi >plus_plus_comm_23 #Hide
-  elim (le_inv_plus_l … Hdi) #Hdim #Hi
-  lapply (ldrop_inv_ldrop1 … H ?) -H // #HLK1
-  elim (IHL12 … HLK1 ? ?) -IHL12 -HLK1 // /2 width=1/ -Hdi -Hide >minus_minus_comm >arith_b1 // /3 width=3/
+lemma l_liftable_LTC: ∀R. l_liftable R → l_liftable (LTC … R).
+#R #HR #K #T1 #T2 #H elim H -T2
+[ /3 width=9/
+| #T #T2 #_ #HT2 #IHT1 #L #d #e #HLK #U1 #HTU1 #U2 #HTU2
+  elim (lift_total T d e) /4 width=11 by step/ (**) (* auto too slow without trace *)
+]
+qed.
+
+lemma l_deliftable_sn_LTC: ∀R. l_deliftable_sn R → l_deliftable_sn (LTC … R).
+#R #HR #L #U1 #U2 #H elim H -U2
+[ #U2 #HU12 #K #d #e #HLK #T1 #HTU1
+  elim (HR … HU12 … HLK … HTU1) -HR -L -U1 /3 width=3/
+| #U #U2 #_ #HU2 #IHU1 #K #d #e #HLK #T1 #HTU1
+  elim (IHU1 … HLK … HTU1) -IHU1 -U1 #T #HTU #HT1
+  elim (HR … HU2 … HLK … HTU) -HR -L -U /3 width=5/
 ]
 qed.
 
@@ -256,25 +235,61 @@ lemma dropable_dx_TC: ∀R. dropable_dx R → dropable_dx (TC … R).
 ]
 qed.
 
+lemma l_deliftable_sn_llstar: ∀R. l_deliftable_sn R →
+                              ∀l. l_deliftable_sn (llstar … R l).
+#R #HR #l #L #U1 #U2 #H @(lstar_ind_r … l U2 H) -l -U2
+[ /2 width=3/
+| #l #U #U2 #_ #HU2 #IHU1 #K #d #e #HLK #T1 #HTU1
+  elim (IHU1 … HLK … HTU1) -IHU1 -U1 #T #HTU #HT1
+  elim (HR … HU2 … HLK … HTU) -HR -L -U /3 width=5/
+]
+qed.
+
 (* Basic forvard lemmas *****************************************************)
 
 (* Basic_1: was: drop_S *)
 lemma ldrop_fwd_ldrop2: ∀L1,I2,K2,V2,e. ⇩[O, e] L1 ≡ K2. ⓑ{I2} V2 →
                         ⇩[O, e + 1] L1 ≡ K2.
 #L1 elim L1 -L1
-[ #I2 #K2 #V2 #e #H lapply (ldrop_inv_atom1 … H) -H #H destruct
+[ #I2 #K2 #V2 #e #H lapply (ldrop_inv_atom1 … H) -H * #H destruct
 | #K1 #I1 #V1 #IHL1 #I2 #K2 #V2 #e #H
-  elim (ldrop_inv_O1 … H) -H * #He #H
+  elim (ldrop_inv_O1_pair1 … H) -H * #He #H
   [ -IHL1 destruct /2 width=1/
   | @ldrop_ldrop >(plus_minus_m_m e 1) // /2 width=3/
   ]
 ]
 qed-.
 
-lemma ldrop_fwd_length: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → |L2| ≤ |L1|.
+lemma ldrop_fwd_length: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → |L1| = |L2| + e.
 #L1 #L2 #d #e #H elim H -L1 -L2 -d -e // normalize /2 width=1/
 qed-.
 
+lemma ldrop_fwd_length_minus2: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → |L2| = |L1| - e.
+#L1 #L2 #d #e #H lapply (ldrop_fwd_length … H) -H /2 width=1/
+qed-.
+
+lemma ldrop_fwd_length_minus4: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → e = |L1| - |L2|.
+#L1 #L2 #d #e #H lapply (ldrop_fwd_length … H) -H //
+qed-.
+
+lemma ldrop_fwd_length_le2: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → e ≤ |L1|.
+#L1 #L2 #d #e #H lapply (ldrop_fwd_length … H) -H //
+qed-.
+
+lemma ldrop_fwd_length_le4: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → |L2| ≤ |L1|.
+#L1 #L2 #d #e #H lapply (ldrop_fwd_length … H) -H //
+qed-.
+
+lemma ldrop_fwd_length_lt2: ∀L1,I2,K2,V2,d,e.
+                            ⇩[d, e] L1 ≡ K2. ⓑ{I2} V2 → e < |L1|.
+#L1 #I2 #K2 #V2 #d #e #H
+lapply (ldrop_fwd_length … H) normalize in ⊢ (%→?); -I2 -V2 //
+qed-.
+
+lemma ldrop_fwd_length_lt4: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → 0 < e → |L2| < |L1|.
+#L1 #L2 #d #e #H lapply (ldrop_fwd_length … H) -H /2 width=1/
+qed-.
+
 lemma ldrop_fwd_lw: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → ♯{L2} ≤ ♯{L1}.
 #L1 #L2 #d #e #H elim H -L1 -L2 -d -e // normalize
 [ /2 width=3/
@@ -283,37 +298,40 @@ lemma ldrop_fwd_lw: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → ♯{L2} ≤ ♯{L1}.
 ]
 qed-.
 
-lemma ldrop_pair2_fwd_fw: ∀I,L,K,V,d,e. ⇩[d, e] L ≡ K. ⓑ{I} V →
-                          ∀T. ♯{K, V} < ♯{L, T}.
-#I #L #K #V #d #e #H #T
-lapply (ldrop_fwd_lw … H) -H #H
-@(le_to_lt_to_lt … H) -H /3 width=1/
+lemma ldrop_fwd_lw_lt: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → 0 < e → ♯{L2} < ♯{L1}.
+#L1 #L2 #d #e #H elim H -L1 -L2 -d -e //
+[ #L #I #V #H elim (lt_refl_false … H)
+| #L1 #L2 #I #V #e #HL12 #_ #_
+  lapply (ldrop_fwd_lw … HL12) -HL12 #HL12
+  @(le_to_lt_to_lt … HL12) -HL12 //
+| #L1 #L2 #I #V1 #V2 #d #e #_ #HV21 #IHL12 #H normalize in ⊢ (?%%); -I
+  >(lift_fwd_tw … HV21) -V2 /3 by lt_minus_to_plus/ (**) (* auto too slow without trace *)
+]
 qed-.
 
-lemma ldrop_fwd_ldrop2_length: ∀L1,I2,K2,V2,e.
-                               ⇩[0, e] L1 ≡ K2. ⓑ{I2} V2 → e < |L1|.
-#L1 elim L1 -L1
-[ #I2 #K2 #V2 #e #H lapply (ldrop_inv_atom1 … H) -H #H destruct
-| #K1 #I1 #V1 #IHL1 #I2 #K2 #V2 #e #H
-  elim (ldrop_inv_O1 … H) -H * #He #H
-  [ -IHL1 destruct //
-  | lapply (IHL1 … H) -IHL1 -H #HeK1 whd in ⊢ (? ? %); /2 width=1/
-  ]
+(* Advanced inversion lemmas ************************************************)
+
+fact ldrop_inv_O2_aux: ∀d,e,L1,L2. ⇩[d, e] L1 ≡ L2 → e = 0 → L1 = L2.
+#d #e #L1 #L2 #H elim H -d -e -L1 -L2
+[ //
+| //
+| #L1 #L2 #I #V #e #_ #_ >commutative_plus normalize #H destruct
+| #L1 #L2 #I #V1 #V2 #d #e #_ #HV21 #IHL12 #H
+  >(IHL12 H) -L1 >(lift_inv_O2_aux … HV21 … H) -V2 -d -e //
 ]
 qed-.
 
-lemma ldrop_fwd_O1_length: ∀L1,L2,e. ⇩[0, e] L1 ≡ L2 → |L2| = |L1| - e.
-#L1 elim L1 -L1
-[ #L2 #e #H >(ldrop_inv_atom1 … H) -H //
-| #K1 #I1 #V1 #IHL1 #L2 #e #H
-  elim (ldrop_inv_O1 … H) -H * #He #H
-  [ -IHL1 destruct //
-  | lapply (IHL1 … H) -IHL1 -H #H >H -H normalize
-    >minus_le_minus_minus_comm //
-  ]
-]
+(* Basic_1: was: drop_gen_refl *)
+lemma ldrop_inv_O2: ∀L1,L2,d. ⇩[d, 0] L1 ≡ L2 → L1 = L2.
+/2 width=4 by ldrop_inv_O2_aux/ qed-.
+
+lemma ldrop_inv_length_eq: ∀L1,L2,d,e. ⇩[d, e] L1 ≡ L2 → |L1| = |L2| → e = 0.
+#L1 #L2 #d #e #H #HL12 lapply (ldrop_fwd_length_minus4 … H) //
 qed-.
 
+lemma ldrop_inv_refl: ∀L,d,e. ⇩[d, e] L ≡ L → e = 0.
+/2 width=5 by ldrop_inv_length_eq/ qed-.
+
 (* Basic_1: removed theorems 50:
             drop_ctail drop_skip_flat
             cimp_flat_sx cimp_flat_dx cimp_bind cimp_getl_conf