Burskii, V.P. and Shtepina Т.V. (2000) “On the Spectrum of an Equivariant Extension of the Laplace Operator in a Ball”, Ukrains’kyi Matematychnyi Zhurnal, 52(11), pp. 1473–1483. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4554 (Accessed: 10 April 2025).