Section Inscribed_angle_2.
Context `{T2D:Tarski_2D}.
Context `{TE:@Tarski_euclidean Tn TnEQD}.

Lemma chord_par_diam : forall O P A B C C' A' U,
O <> P -> ~Col A B C' -> Diam C C' O P -> Midpoint A' A C' -> OnCircle A O P -> OnCircle B O P ->
Col A B U -> Perp O U A B -> Par A C' O U -> B = C.