assert(Par A B A' B').
eapply (midpoint_par A B A' B' M); assumption.
induction H3.
assumption.
spliter.
apply False_ind.
assert(HH:=midpoint_col B' A' B A M).
assert(B <> A /\ Col B' B A /\ Col A' B A).
apply HH.
auto.
apply l7_2.
assumption.
apply l7_2.
assumption.
Col.
spliter.
apply H0.
Col.
Qed.

(* Specifications: *)
Lemma le_left_comm : forall A B C D, Le A B C D -> Le B A C D.
intros.