Proof with finish.
intros.
apply perp_bisect_equiv_def.
unfold Perp_bisect_bis in *.
exists C...
split...
assert_cols; apply l8_14_2_1b_bis...
Qed.

Lemma cong_cop2_perp_bisect_col : forall A B C D E,
Coplanar A C D E ->
Coplanar B C D E ->
Cong C D C E ->
Perp_bisect A B D E ->
Col A B C.