list the judges of beat bobby flay which is also the artist of selections from george gershwin's folk opera porgy and bess ?
SELECT DISTINCT var_uri where brack_open dbr_Beat_Bobby_Flay dbp_judges var_uri sep_dot dbr_Selections_from_George_Gershwin's_Folk_Opera_Porgy_and_Bess dbp_artist var_uri brack_close