VelesnitskiiV. F. and SemenchukV. N. (2012) “On one Shemetkov problem”, Ukrains’kyi Matematychnyi Zhurnal, 64(9), pp. 1282-1288. Available at: http://umj.imath.kiev.ua/index.php/umj/article/view/2658 (Accessed: 17January2021).