+lemma cpg_inv_atom1_drops: ∀c,h,I,G,L,T2. ⦃G, L⦄ ⊢ ⓪{I} ⬈[c, h] T2 →
+ ∨∨ T2 = ⓪{I} ∧ c = 𝟘𝟘
+ | ∃∃s. T2 = ⋆(next h s) & I = Sort s & c = 𝟘𝟙
+ | ∃∃cV,i,K,V,V2. ⬇*[i] L ≡ K.ⓓV & ⦃G, K⦄ ⊢ V ⬈[cV, h] V2 &
+ ⬆*[⫯i] V2 ≡ T2 & I = LRef i & c = cV
+ | ∃∃cV,i,K,V,V2. ⬇*[i] L ≡ K.ⓛV & ⦃G, K⦄ ⊢ V ⬈[cV, h] V2 &
+ ⬆*[⫯i] V2 ≡ T2 & I = LRef i & c = (↓cV) + 𝟘𝟙.
+#c #h * #n #G #L #T2 #H
+[ elim (cpg_inv_sort1 … H) -H *
+ /3 width=3 by or4_intro0, or4_intro1, ex3_intro, conj/
+| elim (cpg_inv_lref1_drops … H) -H *
+ /3 width=10 by or4_intro0, or4_intro2, or4_intro3, ex5_5_intro, conj/
+| elim (cpg_inv_gref1 … H) -H
+ /3 width=1 by or4_intro0, conj/
+]
+qed-.
+