Show the countries that have both perpetrators with injures more than 50 and perpetrators with injures smaller than 20.
return countries ;return perpetrators with injures of #1 ;return the  number of  #2 ;return #1 where #3 is higher than 50 ;return #1 where #3 is lower than 20 ;return #4 ,  #5
['select', 'project', 'aggregate', 'comparative', 'comparative', 'union']