qed-.
(* Basic_1: was: drop1_trans *)
-(* Basic_2A1: includes: drop_trans_ge drop_trans_le drop_trans_ge_comm
+(* Basic_2A1: includes: drop_trans_ge drop_trans_le drop_trans_ge_comm
drops_drop_trans
*)
theorem drops_trans: ∀b1,f1,L1,L. ⇩*[b1,f1] L1 ≘ L →