Borsuk M. V. 1992. “Behaviour of Solutions of the Dirichlet Problem for Quasilinear Elliptical Equations of the Second Order of a General Kind Near Angular Point”. Ukrains’kyi Matematychnyi Zhurnal 44 (2), 167-73. https://umj.imath.kiev.ua/index.php/umj/article/view/7828.