question: What are the names of every person who has a friend over 40 and under 30?
#1 return people 
#2 return friends of #1 
#3 return #1 where #2 is  over 40 
#4 return #1 where #2 is  under 30 
#5 return #1 of both #3 and #4 
#6 return names of #5