DovgosheiA. A., and DordovskiiD. V. “Betweenness Relation and Isometric Imbeddings of Metric Spaces”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 61, no. 10, Oct. 2009, pp. 1319-28, https://umj.imath.kiev.ua/index.php/umj/article/view/3103.