cff-version: 1.2.0
message: If you use results from this problem page, please cite it as below.
title: "Cairn Commons — The chromatic number of the plane (Hadwiger–Nelson problem)"
type: dataset
license: CC-BY-4.0
url: "https://cairn-commons.com/problems/hadwiger-nelson-problem"
date-released: 2026-09-28
authors:
  - name: Cairn Commons contributors
keywords:
  - "combinatorics"
  - "unit-distance-graphs"
  - "graph-colouring"
  - "sat"
  - "discrete-geometry"