Babenko, V. F., and S. A. Pichugov. 2008. “On Kolmogorov-Type Inequalities for Fractional Derivatives of Functions of Two Variables”. Ukrains’kyi Matematychnyi Zhurnal 60 (6), 837–842. https://umj.imath.kiev.ua/index.php/umj/article/view/3200.