Vyhovs’ka, I. Y., Y. B. Zelinskii, and M. V. Tkachuk. “On Some Criteria of Convexity for Compact Sets”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 63, no. 4, Apr. 2011, pp. 466-71, https://umj.imath.kiev.ua/index.php/umj/article/view/2732.