Question: What are the names of the people who are older 40 but no friends under age 30?
SQL: SELECT T1.name FROM Person AS T1 JOIN PersonFriend AS T2 ON T1.name  =  T2.name WHERE T2.friend IN (SELECT name FROM Person WHERE age  >  40) EXCEPT SELECT T1.name FROM Person AS T1 JOIN PersonFriend AS T2 ON T1.name  =  T2.name WHERE T2.friend IN (SELECT name FROM Person WHERE age  <  30)