Show countries where a singer above age 40 and a singer below 30 are from.
return countries ;return singers from  #1 ;return ages of  #2 ;return #1 where #3 is  above 40 ;return #1 where #3 is  below 30 ;return #1 in both #4 and  #5
['select', 'project', 'project', 'comparative', 'comparative', 'intersection']