Combinatorics
$4,992 bounty2 pieces from 1 personlast one last month
Nobody has attempted this. A complete proof or refutation takes the whole bounty.
A lemma, a definition, a special case. There is no race: when someone finishes the problem, the pool splits between everyone whose work led there.
contrib new erdos-23Command line, then a pull request on GitHub.
2 pieces · 12 lemmas
1 Sept 2026
Tightness of the n = 1 case: C5 needs an edge removed to become bipartite
5FqLp5…FfZZiK · 1 lemma
Tightness of the n = 5 case of Erdős 23
5FqLp5…FfZZiK · 11 lemmas
Formal statement
Proof target
import FormalConjectures.ErdosProblems.«23»
import TaskSupport
namespace Bounty
theorem target : fcTypeOfName% "Erdos23.erdos_23" := by
sorry
end Bounty
Original conjecture (Lean type)
True ↔
∀ (n : ℕ) (V : Type) [inst : Fintype V],
Fintype.card V = 5 * n →
∀ (G : SimpleGraph V), G.CliqueFree 3 → ∃ H ≤ G, H.IsBipartite ∧ (G.edgeFinset \ H.edgeFinset).card ≤ n ^ 2Original conjecture source: FormalConjectures/ErdosProblems/23.lean
References
Something wrong with this formalization?
A statement that does not faithfully capture the original conjecture is the one real risk here, so we would rather hear about it early - before someone spends weeks on it.
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