SIEGL, P. PT-Symmetric Laplace-Beltrami Operator in the Strip on a Sphere. Integral Equations and Operator Theory. 2012, 73(1), 5-6. ISSN 0378-620X. E-ISSN 1420-8989. Dostupné z: https://doi.org/10.1007/s00020-011-1932-x