Ltac CopR :=
 let tpoint := constr:(Tpoint) in
 let col := constr:(Col) in
 let cop := constr:(Coplanar) in
   assert_ncols; Cop_refl tpoint col cop.

Lemma l10_15 : forall A B C P, Col A B C -> ~ Col A B P -> exists Q, Perp A B Q C /\ OS A B P Q.