@⦃i, des⦄ ≡ i0 & des ▭ i ≡ des0.
#L1 #L #des #H elim H -L1 -L -des
[ /2 width=7 by ldrops_nil, minuss_nil, at_nil, ex4_3_intro/
-| #L1 #L3 #L #des3 #d #e #_ #HL3 #IHL13 #L2 #i #HL2
+| #L1 #L0 #L #des #d #e #_ #HL0 #IHL0 #L2 #i #HL2
elim (lt_or_ge i d) #Hid
- [ elim (ldrop_trans_le … HL3 … HL2) -L /2 width=2 by lt_to_le/
- #L #HL3 #HL2 elim (IHL13 … HL3) -L3 /3 width=7 by ldrops_cons, minuss_lt, at_lt, ex4_3_intro/
- | lapply (ldrop_trans_ge … HL3 … HL2 ?) -L // #HL32
- elim (IHL13 … HL32) -L3 /3 width=7 by minuss_ge, at_ge, ex4_3_intro/
+ [ elim (ldrop_trans_le … HL0 … HL2) -L /2 width=2 by lt_to_le/
+ #L #HL0 #HL2 elim (IHL0 … HL0) -L0 /3 width=7 by ldrops_cons, minuss_lt, at_lt, ex4_3_intro/
+ | lapply (ldrop_trans_ge … HL0 … HL2 ?) -L // #HL02
+ elim (IHL0 … HL02) -L0 /3 width=7 by minuss_ge, at_ge, ex4_3_intro/
]
]
qed-.
+