The cheat sheet - Need help on understading the subtleties in the book? Just read our convinient, easy to use guide! Separated by chapters, and even with specific page numbers for easy reference! Catch-22 Themes Think about...important themes and imagery in the book. Catch-22 in chronological order - Thank God! Literary Allusion - Heller uses a lot of references to other pieces of literature. Here, their meanng and use is explained. Existentialism - Confused by the constant references to this school of thought?