3 Configurations of 9 Lines with 3 Intersection Points on each Line

Theorem

There exist exactly $3$ essentially different configurations of $9$ straight lines each of which has exactly $3$ points of intersection.

This is one: there are two others.

Proof

This theorem requires a proof. In particular: The precise meaning of the term "essentially different" needs to be established, for a start You can help $\mathsf{Pr} \infty \mathsf{fWiki}$ by crafting such a proof. To discuss this page in more detail, feel free to use the talk page. When this work has been completed, you may remove this instance of {{ProofWanted}} from the code. If you would welcome a second opinion as to whether your work is correct, add a call to {{Proofread}} the page.

Also see

• Pappus's Hexagon Theorem

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $9$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $9$