Find the first name and age of students who have a dog but do not have a cat as a pet.
return students ;return pets of  #1 ;return #1 where #2 is  dog ;return #1 where #2 is  not  cat ;return #1 of  both #3 and  #4 ;return first names of  #5 ;return ages of  #5 ;return #6 ,  #7
['select', 'project', 'comparative', 'comparative', 'intersection', 'project', 'project', 'union']