Postulates for Separation of Point-Pairs (Reversible Order on a Closed Line) Edward V. Huntington and Kurt E. Rosinger Proceedings of the American Academy of Arts and Sciences , pp. 61-145 (85 pages) ...

We completely settle the questions about implications between the three versions of the parallel postulate. The strong parallel postulate easily implies Euclid 5, and Euclid 5 also implies the strong ...