4.1. Oh, That's Easy!4.2. One, Two, Many4.3. Mirror, Mirror4.4. Designing with Induction (and Recursion)4.4.1. Finding a Maximum Permutation4.4.2. The Celebrity Problem4.4.3. Topological Sorting4.5. Stronger Assumptions4.6. Invariants and Correctness4.7. Relaxation and Gradual Improvement4.8. Reduction + Contraposition = Hardness Proof4.9. Problem Solving Advice4.10. Summary4.11. If You're Curious ...4.12. Exercises4.13. References