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@alphacolony alphacolony commented Jan 18, 2026

Adds a formalization of Erdős Problem 794 (disproved; see erdosproblems.com/794). Hope this is a good fit for the repository’s “short counterexample / not a lengthy proof” guideline but I'm happy to adjust if you’d prefer a different level of abstraction. Completed with the assistance of Harmonic's Aristotle and Claude Opus 4.5.

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google-cla bot commented Jan 18, 2026

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@github-actions github-actions bot added the erdos-problems Erdős Problems label Jan 18, 2026
Comment on lines 91 to 99
/-- Harris's counterexample has exactly 28 edges. -/
@[category test, AMS 5]
theorem harrisCounterexample_card : HarrisCounterexample.card = 28 := by native_decide

/-- Harris's counterexample is 3-uniform. -/
@[category test, AMS 5]
theorem harrisCounterexample_is3Uniform : Is3Uniform HarrisCounterexample := by
unfold Is3Uniform
native_decide
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Can these be closed with decide or decide +kernel ?

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Tried decide / decide +kernel, but it hit maxRecDepth during lake build.

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Done, ran this morning and avoided maxRecDepth

Comment on lines +71 to +72
∃ (S : Finset α) (_ : S ∈ Finset.univ.powersetCard k),
(H.filter (fun e => e ⊆ S)).card ≥ m
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Suggested change
∃ (S : Finset α) (_ : S ∈ Finset.univ.powersetCard k),
(H.filter (fun e => e ⊆ S)).card ≥ m
∃ S : Finset α, #S = k \and #{e \in H | e ⊆ S} ≥ m

You will need open Finset first

Comment on lines +126 to +127
-- `answer(False)` is `False`, so this is equivalent to `¬ Statement`.
simp only [false_iff]
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Suggested change
-- `answer(False)` is `False`, so this is equivalent to `¬ Statement`.
simp only [false_iff]
simp?

and see what it comes up with

@YaelDillies YaelDillies added the awaiting-author The author should answer a question or perform changes. Reply when done. label Jan 22, 2026
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3 participants