BurskiiV. P., & ShtepinaТ. V. (2000). On the Spectrum of an Equivariant Extension of the Laplace Operator in a Ball. Ukrains’kyi Matematychnyi Zhurnal, 52(11), 1473-1483. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4554