@article{VMUMM_1991_4_a7,
     author = {K. I. Tyurin},
     title = {Extremal properties of simple eigenvalues of the {Laplace} operator with {Dirichlet} boundary conditions on a ball},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {33--37},
     publisher = {mathdoc},
     number = {4},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1991_4_a7/}
}