who is the common prime minster of frederick stanleyr and robert gascoyne-cecil ?
SELECT DISTINCT var_uri where brack_open dbr_Frederick_Stanley,_16th_Earl_of_Derby dbo_primeMinister var_uri sep_dot dbr_Robert_Gascoyne-Cecil,_3rd_Marquess_of_Salisbury dbp_primeminister var_uri brack_close