There has been a murder! We've taken statements from four suspects:
Miss Henson says: "I'm innocent!"
General Mattis says: "Professor Bernstein is guilty!"
Mrs. Humphrey says: "General Mattis is guilty!"
Professor Bernstein says: "I'm innocent!"
Only one of them is telling the truth. You must determine which one.

suspect('Miss Henson', 1).
suspect('General Mattis', 2).
suspect('Mrs. Humphrey', 3).
suspect('Professor Bernstein', 4).