inductive cpysa: ynat → ynat → relation4 genv lenv term term ≝
| cpysa_atom : ∀I,G,L,d,e. cpysa d e G L (⓪{I}) (⓪{I})
| cpysa_subst: ∀I,G,L,K,V1,V2,W2,i,d,e. d ≤ yinj i → i < d+e →
- ⇩[0, i] L ≡ K.ⓑ{I}V1 → cpysa 0 (⫰(d+e-i)) G K V1 V2 →
+ ⇩[i] L ≡ K.ⓑ{I}V1 → cpysa 0 (⫰(d+e-i)) G K V1 V2 →
⇧[0, i+1] V2 ≡ W2 → cpysa d e G L (#i) W2
| cpysa_bind : ∀a,I,G,L,V1,V2,T1,T2,d,e.
cpysa d e G L V1 V2 → cpysa (⫯d) e G (L.ⓑ{I}V2) T1 T2 →
[ #I #G #L #d #e #X #H
elim (cpy_inv_atom1 … H) -H // * /2 width=7 by cpysa_subst/
| #I #G #L #K #V1 #V2 #W2 #i #d #e #Hdi #Hide #HLK #_ #HVW2 #IHV12 #T2 #H
- lapply (ldrop_fwd_ldrop2 … HLK) #H0LK
+ lapply (ldrop_fwd_drop2 … HLK) #H0LK
lapply (cpy_weak … H 0 (d+e) ? ?) -H // #H
elim (cpy_inv_lift1_be … H … H0LK … HVW2) -H -H0LK -HVW2
/3 width=7 by cpysa_subst, ylt_fwd_le_succ/
lemma cpys_ind_alt: ∀R:ynat→ynat→relation4 genv lenv term term.
(∀I,G,L,d,e. R d e G L (⓪{I}) (⓪{I})) →
(∀I,G,L,K,V1,V2,W2,i,d,e. d ≤ yinj i → i < d + e →
- ⇩[O, i] L ≡ K.ⓑ{I}V1 → ⦃G, K⦄ ⊢ V1 ▶*×[O, ⫰(d+e-i)] V2 →
+ ⇩[i] L ≡ K.ⓑ{I}V1 → ⦃G, K⦄ ⊢ V1 ▶*×[O, ⫰(d+e-i)] V2 →
⇧[O, i+1] V2 ≡ W2 → R O (⫰(d+e-i)) G K V1 V2 → R d e G L (#i) W2
) →
(∀a,I,G,L,V1,V2,T1,T2,d,e. ⦃G, L⦄ ⊢ V1 ▶*×[d, e] V2 →