Formal Verification with KeY: A Tutorial Bernhard Beckert, Reiner Hähnle, Martin Hentschel, and Peter H. Schmitt This chapter of the KeY Book gives a systematic tutorial introduction on how to perform formal program verification with the KeY system. It illustrates a number of complications and pitfalls, notably programs with loops, and shows how to deal with them. After working through this tutorial, you should be able to formally verify with KeY the correctness of simple Java programs, such as standard sorting algorithms, gcd, etc.