elim (cpxs_inv_lref1 … H) -H /2 width=1/
* #I0 #K0 #V0 #U0 #HLK0 #HVU0 #HU0
lapply (ldrop_mono … HLK0 … HLK) -HLK0 #H destruct
-lapply (ldrop_fwd_ldrop2 … HLK) -HLK /3 width=9/
+lapply (ldrop_fwd_drop2 … HLK) -HLK /3 width=9/
qed-.
lemma cpxs_fwd_theta: ∀h,g,a,G,L,V1,V,T,U. ⦃G, L⦄ ⊢ ⓐV1.ⓓ{a}V.T ➡*[h, g] U →