AldashevS. A. (2011). Eigenvalues and eigenfunctions of the Gellerstedt problem for the multidimensional Lavrent?ev?Bitsadze equation. Ukrains’kyi Matematychnyi Zhurnal, 63(6), 827-832. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/2765