Vyhovs'ka, I. Yu., Yu. B. Zelinskii, and M. V. Stefanchuk. 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.