The Smullyan Trilogy

Raymond M. Smullyan: Gödel's Incompleteness Theorems.
Oxford Logic Guides 19. Oxford 1992

Raymond M. Smullyan: Recursion Theory for Metamathematics.
Oxford Logic Guides 22. Oxford 1993

Raymond M. Smullyan: Diagonalization and Self-Reference.
Oxford Logic Guides 27. Oxford 1994