Question: Please tell me the names of the person who has friends with age above 40 and 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 )  INTERSECT 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 )