Bakhtin, A. K., & Targonskii, A. L. (2011). Generalized (n, d)-ray systems of points and inequalities for nonoverlapping domains and open sets. Ukrains’kyi Matematychnyi Zhurnal, 63(7), 867-879. https://umj.imath.kiev.ua/index.php/umj/article/view/2771