AldashevS. A. “Well-Posedness of the Dirichlet and Poincaré Problems for the Wave Equation in a Many-Dimensional Domain”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 66, no. 10, Oct. 2014, pp. 1414–1419, https://umj.imath.kiev.ua/index.php/umj/article/view/2232.