qed-.
(* Basic_2A1: was: lpx_sn_dropable *)
lemma lex_dropable_dx (R): dropable_dx R.
#R #L1 #L2 * #f2 #Hf2 #HL12 #b #f #K2 #HLK2 #Hf
elim (sex_co_dropable_dx … HL12 … HLK2) -L2
qed-.
(* Basic_2A1: was: lpx_sn_dropable *)
lemma lex_dropable_dx (R): dropable_dx R.
#R #L1 #L2 * #f2 #Hf2 #HL12 #b #f #K2 #HLK2 #Hf
elim (sex_co_dropable_dx … HL12 … HLK2) -L2