Erdős Problem 501 after adding ω₂ random reals

Elliot Glazer, Sol

A ZFC model has the property that every family (Aₓ) of subsets of ℝ with outer measure below one admits an infinite X such that x∉Aᵧ for distinct x,y∈X. Combined with Hechler’s earlier CH counterexample, this gives relative ZFC independence for the first question of Erdős 501.

Sources for this record

What was already known

Hechler supplied the CH negative direction. Lee’s earlier positive result used a real-valued-measurable-cardinal or full-measure-extension hypothesis; the closed-set second question was already solved.

AI involvement AI-centered

Glazer chose the problem and forcing route. The disclosure credits GPT-5.6 Sol with the central transfer argument and Claude models with Lean code under his direction; no independent human peer review is reported.

Sol supplied the central transfer argument within Glazer's human-directed set-theoretic program; Claude supplied the formal code.

Importance Notable

Removes the large-cardinal assumption from the positive direction of a set-theory problem.

Limitations

The Lean project proves the positive model through a c⁺-coordinate random algebra, distinct from the paper’s ω₂-random-reals-over-CH route. Hechler’s negative direction and the closed-set question are earlier human results.

Technical verification Formal (Lean 4.34.0-rc1 with Mathlib and Flypitch4; Comparator and axiom audits)

The cited status reports kernel-checked positive-model, independence and sentence-faithfulness targets with standard axioms and two Comparator configurations. The machine proof verifies the result through a changed random-forcing route, not the draft's literal omega_2-over-CH proof. This is source-reported, not reproduced here.

Independent checking

Pinned Lean build without sorry, standard-axiom audit, and both Mathlib-only and Flypitch Comparator challenges

Checker
Lean kernel and Comparator in Glazer's pinned repository
Scope
Positive ZFC model for Erdős 501's first question, independence targets and first-order sentence-faithfulness bridge
Basis
Reported by the linked checker
Evidence source

Human understanding Few

Default for missing evidence: Glazer chose the route and reviewed mathematics, but a human explanation of the core transfer and complete understanding of its mechanism is not documented.

Correction and publication history

2026-10-18 · publication

Removes the large-cardinal assumption from the positive direction of a set-theory problem.

Read this published revision