## 15-212: Principles of Programming |

We demonstrate a complicated representation invariant using Red/Black Trees. The main lesson is to understand the subtle interactions of invariants, data structures, and reliable code production. In order to write code satisfying a strong invariant, it is useful to proceed in stages. Each stage satisfies a simple invariant, and is provably correct. Together the stages satisfy the strong invariant.

- Representation invariants
- Weakening an invariant temporarily

- Chapter 20: Signature Ascription
- Chapter 32: Data Abstraction

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