Show the theme for exhibitions with both records of an attendance below 100 and above 500.
return exhibitions ;return attendances of #1 ;return number of  #2 for each #1 ;return #1 where #3 is  below 100 ;return #1 where #3 is  above 500 ;return #1 of both #4 and #5 ;return themes for #6
['select', 'project', 'group', 'comparative', 'comparative', 'intersection', 'project']