On M. T. Calapso's characterization of the metric of an absolute plane
The authors describe the importance of M. T. Calapso's axiom for the axiomatization of hyperbolic planes by means of the midpoint relation alone and also for the axiomatization of metric planes. They show the equivalence between Calapso's axiom and the rectangle existence axiom under two fairly weak axiom systems, one is a fragment of an axiom system proposed by K. Sörensen for nonelliptic metric planes, the second is the axiom system for Wolff planes.
scientific article; zbMATH DE number 5562636