Vyhovs’kaI. Yu., ZelinskiiYu. B., and StefanchukM. V. 2015. “Generalized Convex Sets and the problem of Shadow”. Ukrains’kyi Matematychnyi Zhurnal 67 (12), 1658-66. https://umj.imath.kiev.ua/index.php/umj/article/view/2098.