Please help me to solve the following question with a SQL statement

The table of User is defined as:

details: a user can follow another user (e.g. user1 can follow user2, and user2 can follow user1)

Question: Write an SQL statement to produce a list of paired users who are following each other mutually. (for example, user1 is following user2 and user2 is following user1)

table name user User ID fields in table User Name Follows