Suppose that ABCD is a cyclic quadrilateral and CD\equal{}DA. Points E and F belong to the segments AB and BC respectively, and \angle ADC\equal{}2\angle EDF. Segments DK and DM are height and median of triangle DEF, respectively. L is the point symmetric to K with respect to M. Prove that the lines DM and BL are parallel. geometryincenternumber theorygreatest common divisorcyclic quadrilateralgeometry proposed