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← Ch. 5: Rigor Check Table of contents Ch. 7: Group Theorems →

Learning objectives. By the end of this chapter, translate the mathematical definition of a group into a Lean structure field by field, build both an abelian (Int) and a genuinely non-abelian (permutations of Fin 3) example from scratch, and articulate why bundling data with proof obligations pays off once theorems are proved generically (Chapter 7).

Sections

  1. The mathematical definition
  2. Translating the definition into a Lean structure
  3. A first example: the integers under addition
  4. A non-abelian example: permutations of three elements
  5. Accessing the fields
  6. Why bundle proofs with data at all?
  7. Exercises

Starting with this chapter, most examples are followed by a “Mathlib equivalent” box (see 00-setup/04-mathlib-note.md). For links to the official docs for every Mathlib name used in those boxes, see the tactic and library reference.


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