Skip to content

Erdős problem 209

Let AA be a finite collection of d4d\geq 4 non-parallel lines in R2\mathbb{R}^2 such that there are no points where at least four lines from AA meet. Must there exist a 'Gallai triangle' (or 'ordinary triangle'): three lines from AA which intersect in three points, and each of these intersection points only intersects two lines from AA?

Workspace

Open this exact Problem, source revision, and authority Repository in Workbench. This handoff does not clone, switch, upload, or execute anything.

Canvas

public preview
  1. Source#209
  2. ResultNone
  3. Checks0

Reported activity

Work these sources record against this Problem. Source-reported attribution, not reviewed here.

Search problems.science

Find a Problem, Result, source, or page