What is the first name of the students who are in age 20 to 25 and living in PHL city?
return students ;return ages of #1 ;return #1 where #2 is  at least 20 ;return #1 where #2 is  at most 25 ;return cities of both #3 and #4 ;return #1 where #5 is  PHL ;return first names of #6
['select', 'project', 'comparative', 'comparative', 'intersection', 'comparative', 'project']