Proof of `Triangles are maximal outerplanar`

groundedproofs/Lax68Proofs/Triangles.lean · lax-68

What this proof establishes

no assumptions

Assuming the claims on the left, the claim on the right holds — checked by the archive's pipeline. Proof code is not displayed here.

Read the Lean proof on GitHub

Description

A triangle is transported to three explicit points on the unit circle. The three sides do not cross, so this is an outerplane drawing. Completeness makes the graph maximal: no further edge can be added on the same vertices.