IMO 2004 Problem 1

Let $ABC$ be an acute-angled triangle with $AB\neq AC$ . The circle with diameter $BC$ intersects the sides $AB$ and $AC$ at $M$ and $N$ respectively. Denote by $O$ the midpoint of the side $BC$ . The bisectors of the angles $\angle BAC$ and $\angle MON$ intersect at $R$ . Prove that the circumcircles of the triangles $BMR$ and $CNR$ have a common point lying on the side $BC$ .

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