@article{IVM_1958_2_a11,
     author = {I. S. Kats and M. G. Krein},
     title = {Criteria for the discreteness of the spectrum of a~singular string},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {136--153},
     publisher = {mathdoc},
     number = {2},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1958_2_a11/}
}