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Erdős problem 501

For every x∈Rx \in \mathbb{R} let Ax⊂RA_x \subset \mathbb{R} be a bounded set of Lebesgue outer measure <1< 1. Must there be an infinite independent set, that is an infinite X⊆RX \subseteq \mathbb{R} with x∉Ayx \notin A_y for all distinct x,y∈Xx, y \in X?

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FormalConjectures/ErdosProblems/

501.lean

Retained formal statement1 of 13

For every x∈Rx \in \mathbb{R} let Ax⊂RA_x \subset \mathbb{R} be a bounded set with outer measure <1< 1. Must there exist an infinite independent set, that is, some infinite X⊆RX \subseteq \mathbb{R} such that x∉Ayx \notin A_y for all x≠y∈Xx \neq y \in X?

If the sets AxA_x are closed and have measure <1< 1, then must there exist an independent set of size 33?

Known results: Erdős–Hajnal [ErHa60] proved the existence of arbitrarily large finite independent sets. Hechler [He72] showed the answer is no assuming the continuum hypothesis.

FormalConjectures/ErdosProblems/501.leanErdos501.erdos_5014 linesExact file
True ↔  ∀ (A : ℝ → Set ℝ),    (∀ (x : ℝ), Bornology.IsBounded (A x)) →      (∀ (x : ℝ), MeasureTheory.volume.toOuterMeasure (A x) < 1) → ∃ X, X.Infinite ∧ X.Pairwise fun x y => x ∉ A y
OpenStatement only, no proof