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Chapter 30: Lubell, Katona, Hall, and sharpness proofs - #177
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October 12, 2026 10:45
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Expand Chapter 30, "Three famous theorems on finite sets," with the supplied Lean source. Add Lubell's chain-counting argument and the LYM inequality, Katona's cyclic-permutation counting argument, and the finite inductive proof of Hall's marriage theorem. Include sharpness statements, extremal intersecting families, and the n=4, k=2 example while preserving the existing three main theorem interfaces.
Replace the umbrella Mathlib import with targeted dependencies and adjust long lines to meet repository style.
Validation on commit 9971428: Lean compilation, declaration lint, style lint,
git diff --check, blueprint generation and declaration checks, and API documentation all pass. Full CI: https://github.com/mo271/FormalBook/actions/runs/38237671399.A source scan found no sorry/admit, new mathematical axioms, or native_decide in the supplied chapter. Complete chapter coverage and fidelity to the book have not been independently reviewed.