VelichkoI. G. and StegantsevaP. G. (2010) “Example of a function of two variables that cannot be an $R$-function”, Ukrains’kyi Matematychnyi Zhurnal, 62(2), pp. 270–274. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/2863 (Accessed: 23November2024).