  We have studied events with a high-x_F antiproton and two central jets with
E_T>7 GeV in CDF, in p+p_bar collisions at sqrt(s) = 1800 GeV. From the di-jet
kinematics we derive the diffractive structure function of the antiproton. We
also find an excess of events with a rapidity gap at least 3.5 units wide in
the proton direction, which we interpret as di-jet production in double pomeron
exchange events. We find non-factorization between our single diffractive
results and (a) diffraction in ep at HERA (b) double pomeron exchange.
