(* Inversion lemmas with degree-based equivalence for terms *****************)
-lemma cpm_tdeq_inv_lref (n) (h) (o) (G) (L) (i):
- ∀X. ⦃G, L⦄ ⊢ #i ➡[n,h] X → #i ≛[h,o] X →
- ∧∧ X = #i & n = 0.
+lemma cpm_tdeq_inv_lref_sn (n) (h) (o) (G) (L) (i):
+ ∀X. ⦃G,L⦄ ⊢ #i ➡[n,h] X → #i ≛[h,o] X →
+ ∧∧ X = #i & n = 0.
#n #h #o #G #L #i #X #H1 #H2
lapply (tdeq_inv_lref1 … H2) -H2 #H destruct
elim (cpm_inv_lref1_drops … H1) -H1 // * [| #m ]
#K #V1 #V2 #_ #_ #H -V1
elim (lifts_inv_lref2_uni_lt … H) -H //
qed-.
+
+lemma cpm_tdeq_inv_atom_sn (n) (h) (o) (I) (G) (L):
+ ∀X. ⦃G,L⦄ ⊢ ⓪{I} ➡[n,h] X → ⓪{I} ≛[h,o] X →
+ ∨∨ ∧∧ X = ⓪{I} & n = 0
+ | ∃∃s. X = ⋆(next h s) & I = Sort s & n = 1 & deg h o s 0.
+#n #h #o * #s #G #L #X #H1 #H2
+[ elim (cpm_inv_sort1 … H1) -H1
+ cases n -n [| #n ] #H #Hn destruct
+ [ /3 width=1 by or_introl, conj/
+ | elim (tdeq_inv_sort1 … H2) -H2 #x #d #Hs
+ <(le_n_O_to_eq n) [| /2 width=3 by le_S_S_to_le/ ] -n #Hx #H destruct
+ lapply (deg_next … Hs) #H
+ lapply (deg_mono … H Hx) -H -Hx #Hd
+ lapply (pred_inv_fix_sn … Hd) -Hd #H destruct
+ /3 width=4 by refl, ex4_intro, or_intror/
+ ]
+| elim (cpm_tdeq_inv_lref_sn … H1 H2) -H1 -H2 /3 width=1 by or_introl, conj/
+| elim (cpm_inv_gref1 … H1) -H1 -H2 /3 width=1 by or_introl, conj/
+]
+qed-.