list the common prime minister of the william whitelaw and john macgregor ?
SELECT DISTINCT var_uri where brack_open dbr_William_Whitelaw,_1st_Viscount_Whitelaw dbo_primeMinister var_uri sep_dot dbr_John_MacGregor,_Baron_MacGregor_of_Pulham_Market dbo_primeMinister var_uri brack_close