KhachatryanA. Kh., and KhachatryanKh. A. “Letter to the Editor”. Ukrains’kyi Matematychnyi Zhurnal 62, no. 6 (June 25, 2010): 865. Accessed December 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2919.