#I1 #I2 #L1 #L2 #V1 #V2 #d #e #HL12 #Hd <(ylt_inv_O1 … Hd) /2 width=1 by lsuby_succ/
qed.
+lemma lsuby_pair_O_Y: ∀L1,L2. L1 ⊑×[0, ∞] L2 →
+ ∀I1,I2,V. L1.ⓑ{I1}V ⊑×[0,∞] L2.ⓑ{I2}V.
+#L1 #L2 #HL12 #I1 #I2 #V lapply (lsuby_pair I1 I2 … V … HL12) -HL12 //
+qed.
+
lemma lsuby_refl: ∀L,d,e. L ⊑×[d, e] L.
#L elim L -L //
#L #I #V #IHL #d elim (ynat_cases … d) [| * #x ]
#He destruct /2 width=1 by lsuby_zero, lsuby_pair/
qed.
-lemma lsuby_length: ∀L1,L2. |L2| ≤ |L1| → L1 ⊑×[yinj 0, yinj 0] L2.
-#L1 elim L1 -L1
-[ #X #H lapply (le_n_O_to_eq … H) -H
- #H lapply (length_inv_zero_sn … H) #H destruct /2 width=1 by lsuby_atom/
-| #L1 #I1 #V1 #IHL1 * normalize
- /4 width=2 by lsuby_zero, le_S_S_to_le/
+lemma lsuby_O2: ∀L2,L1,d. |L2| ≤ |L1| → L1 ⊑×[d, yinj 0] L2.
+#L2 elim L2 -L2 // #L2 #I2 #V2 #IHL2 * normalize
+[ #d #H lapply (le_n_O_to_eq … H) -H <plus_n_Sm #H destruct
+| #L1 #I1 #V1 #d #H lapply (le_plus_to_le_r … H) -H #HL12
+ elim (ynat_cases d) /3 width=1 by lsuby_zero/
+ * /3 width=1 by lsuby_succ/
]
qed.
lemma lsuby_sym: ∀d,e,L1,L2. L1 ⊑×[d, e] L2 → |L1| = |L2| → L2 ⊑×[d, e] L1.
#d #e #L1 #L2 #H elim H -d -e -L1 -L2
[ #L1 #d #e #H >(length_inv_zero_dx … H) -L1 //
-| /2 width=1 by lsuby_length/
+| /2 width=1 by lsuby_O2/
| #I1 #I2 #L1 #L2 #V #e #_ #IHL12 #H lapply (injective_plus_l … H)
/3 width=1 by lsuby_pair/
| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #IHL12 #H lapply (injective_plus_l … H)
#L1 #L2 #d #e #H elim H -L1 -L2 -d -e normalize /2 width=1 by le_S_S/
qed-.
-lemma lsuby_fwd_ldrop2_be: ∀L1,L2,d,e. L1 ⊑×[d, e] L2 →
- ∀I2,K2,W,s,i. ⇩[s, 0, i] L2 ≡ K2.ⓑ{I2}W →
- d ≤ i → i < d + e →
- ∃∃I1,K1. K1 ⊑×[0, ⫰(d+e-i)] K2 & ⇩[s, 0, i] L1 ≡ K1.ⓑ{I1}W.
+(* Properties on basic slicing **********************************************)
+
+lemma lsuby_ldrop_trans_be: ∀L1,L2,d,e. L1 ⊑×[d, e] L2 →
+ ∀I2,K2,W,s,i. ⇩[s, 0, i] L2 ≡ K2.ⓑ{I2}W →
+ d ≤ i → i < d + e →
+ ∃∃I1,K1. K1 ⊑×[0, ⫰(d+e-i)] K2 & ⇩[s, 0, i] L1 ≡ K1.ⓑ{I1}W.
#L1 #L2 #d #e #H elim H -L1 -L2 -d -e
[ #L1 #d #e #J2 #K2 #W #s #i #H
elim (ldrop_inv_atom1 … H) -H #H destruct