Let ABCDABCD be a convex quadrilateral such that AC=BDAC = BD and the sides ABAB and CDCD are not parallel. Let PP be the intersection point of the diagonals ACAC and BDBD. Points EE and FF lie, respectively, on segments BPBP and APAP such that PC=PEPC = PE and PD=PFPD = PF. Prove that the circumcircle of the triangle determined by the lines ABAB, CDCD and EFEF is tangent to the circumcircle of the triangle ABPABP.