Exercise 1. Alice, Bernard, Cédric, and Diane were playing tennis in the yard. Suddenly, the ball broke the neighbor's window. Furious, the neighbor approached the four children.

Alice said: "It wasn't me!". Bernard said: "It was Diane". Cédric said: "No, it was Bernard". Diane said: "Bernard lied".

Assuming that exactly one of the four children told the truth, which one of them broke the neighbor's window?
Solution to Exercise 1 If D lies, then B tells the truth, so Diane is guilty. Since exactly one of the children told the truth, A lied, so she is guilty, which is contradictory.

We deduce that D told the truth and that A, B, C are liars. Since A lied, we conclude that Alice broke the window.