Every two-coloring of the plane misses at most one triangle, which is equilateral

In every arbitrary two-coloring of the Euclidean plane, each non-equilateral three-point set, including three distinct collinear points, has a monochromatic congruent copy. At most one equilateral side length can be missed, and an alternating-strip coloring shows that one exception can occur.

Sources for this record

What was already known

Shader proved the right-triangle case; later work treated further triangle families and restricted colorings. The new proof adapts OpenAI’s wild-character rigidity and measurable-transfer machinery, extending its carrier field to handle arbitrary real side-length ratios.

AI involvement AI-autonomous

Plasma AI reports unattended alternating research runs by GPT-6 Astra and Claude Opus 5.5 that found the argument. Human direction covered the target and formalization/publication setup; no human mathematical proof input is recorded. The original research contribution, rather than the later formalization management, supports AI-autonomous.

Importance Notable

Resolves the specified longstanding Erdős question, subject to the stated scope. The earlier theorems and later human work retain their credit.

Limitations

Copies allow rotations, reflections and relabelling, but not rescaling. This is the triangle-by-triangle statement: it does not show that one fixed color contains every triangle. That stronger Erdős–Graham formulation remains open. The prose and formalization were produced by AI; the human lead checked three source-matched statements, not the two added variants or the complete proof.

Technical verification Formal (Lean)

Palomar reports exact selected-statement comparison and kernel checking with Lean, NanoDa and con-ron on 19 October. No local proof rebuild was performed.

Formal checking

Palomar reports exact selected-statement comparison and kernel checking with Lean, NanoDa and con-ron on 19 October. No local proof rebuild was performed.

Checker
Palomar: Lean, NanoDa and con-ron
Scope
Five selected theorems, including arbitrary two-colorings, at most one missing triangle, the non-equilateral case and three distinct collinear points; Mathlib definitions and only standard Lean axioms.
Basis
Reported by the linked checker
Check date
2026-10-19
Evidence source

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

Human understanding Few

Few is the default when evidence for a higher level is insufficient. The available blueprint and proof reviews are AI-produced. Human statement correspondence checks do not document a human explanation of the central argument. Few is the evidence default.

Correction and publication history

2026-10-19 · publication

Added this sourced contribution with its stated scope, AI attribution, checking evidence and research limits.

Read this published revision