-lemma drops_pair2_fwd_rfw: ∀I,L,K,V,s,t. ⬇*[s, t] L ≡ K.ⓑ{I}V → ∀T. ♯{K, V} < ♯{L, T}.
-#I #L #K #V #s #t #HLK lapply (drops_fwd_lw … HLK) -HLK
+lemma drops_pair2_fwd_rfw: ∀I,L,K,V,c,f. ⬇*[c, f] L ≡ K.ⓑ{I}V → ∀T. ♯{K, V} < ♯{L, T}.
+#I #L #K #V #c #f #HLK lapply (drops_fwd_lw … HLK) -HLK