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KöMaL 2016 A682

    Let A1B1C1D1E1F1A2B2C2D2E2F2A_1B_1C_1D_1E_1F_1A_2B_2C_2D_2E_2F_2 be a cyclic dodecagon such that its diagonals A1A2A_1A_2, B1B2B_1B_2 and C1C2C_1C_2 are concurrent, the diagonals A1A2A_1A_2, E1E2E_1E_2 and F1F2F_1F_2 are concurrent, the diagonals C1C2C_1C_2, D1D2D_1D_2 and E1E2E_1E_2 are concurrent, and finally the diagonals B1B2B_1B_2, D1D2D_1D_2 and F1F2F_1F_2 are concurrent.Let kAk_A, kCk_C and kEk_E be three circular arcs in the interior of the dodecagon's circumcircle such that kAk_A connects A1A_1 and A2A_2, kCk_C connects C1C_1 and C2C_2, and kEk_E connects E1E_1 and E2E_2. Let the intersection points of the three arcs be B=kA∩kCB=k_A\cap k_C, D=kC∩kED=k_C\cap k_E and F=kA∩kEF=k_A\cap k_E. Prove that the circular arcs B1BB2B_1BB_2, D1DD2D_1DD_2 and F1FF2F_1FF_2 are concurrent. (These arcs degenerate to line segments if their specified points are collinear.)

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