Local Odd-Cycle Transversals in Generalized Mycielski Graphs and an Erdős Problem on Almost-Half Independent Sets

Przemek Chojecki, GPT-5.5 Pro

An infinite-chromatic graph has the property that, for every nonnegative function f(m) tending to infinity, every m-vertex finite subgraph contains an independent set of size at least m/2−f(m). A stronger construction bounds local odd-cycle-transversal number by any prescribed unbounded integer profile.

Sources for this record

What was already known

Erdős, Hajnal and Szemerédi had a linear-error almost-half bound. The arbitrary slowly growing additive-error question was open; Stiebitz’s chromatic theorem is a prior input.

AI involvement AI-led

Przemek Chojecki and GPT-5.5 Pro are credited as coauthors. Chojecki presents the argument; paws and plby later formalized its construction and Stiebitz input.

GPT-5.5 Pro is credited as an author of the mathematical note; no log shows the little-human-input independence needed for AI-autonomous.

Importance Notable

The construction answers the arbitrary-additive-error question and strengthens the local graph property.

Limitations

The original note does not separate Chojecki’s and GPT-5.5 Pro’s discovery steps. A later Lean file reports a matching theorem, including the Stiebitz input.

Technical verification Formal (Lean 4)

A later Lean file states the nonnegative-function version of the same claim and reports only Lean's standard foundational axioms; its conditional construction and Stiebitz theorem are both proved there. This is a third-party, source-reported machine check, not a build reproduced here.

Formal checking

Lean proof of erdos_750_independence and erdos_750, including the previously assumed Stiebitz lower bound

Checker
Lean 4, formalizations by paws and plby, vendored by Jayyhk
Scope
Erdős #750 for every nonnegative real-valued f tending to infinity, via the infinite-chromatic local odd-cycle-transversal construction
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Full

The note explains the projection inequality, postponement of apex odd cycles, finite profile induction, and disjoint-union argument.

Correction and publication history

2026-10-18 · publication

The construction answers the arbitrary-additive-error question and strengthens the local graph property.

Read this published revision