Proof with finish.
intros A B C X1 X2 X3 HNC HPar1 HPar2 HPar3.
apply cop_npar__inter_exists.
apply coplanar_perm_2, coplanar_trans_1 with C; Col; Cop.
intro HNPar; apply HNC.
assert (HFalsePar : Par B C A C)
by (apply (par_trans B C B X1 A C); finish; apply (par_trans B C A X3 B); finish).
apply par_id_2...
Qed.

Lemma diff_not_col_col_par4_mid: forall A B C D E,
D <> E -> ~ Col A B C -> Col C D E -> Par A B C D ->
Par A B C E -> Par A E B C -> Par A C B D -> Midpoint C D E.