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BALKAN-SL 2016 G3

    Given that ABCA B C is a triangle where AB<ACA B<A C. On the half-lines BAB A and CAC A we take points FF and EE respectively such that BF=CE=BCB F=C E=B C. Let M,NM, N and HH be the mid-points of the segments BF,CEB F, C E and BCB C respectively and KK and OO be the circumcircles of the triangles ABCA B C and MNHM N H respectively. We assume that OKO K cuts BEB E and HNH N at the points A1A_{1} and B1B_{1} respectively and that C1C_{1} is the point of intersection of HNH N and FEF E. If the parallel line from A1A_{1} to OC1O C_{1} cuts the line FEF E at DD and the perpendicular from A1A_{1} to the line DB1D B_{1} cuts FEF E at the point M1M_{1}, prove that EE is the orthocenter of the triangle A1OM1A_{1} O M_{1}.

    Dataset text NuminaMath olympiads. Quoted with source.

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