@article{SM_1985_51_2_a4,
     author = {A. S. Markus and V. I. Matsaev},
     title = {A~theorem on comparison of spectra, and spectral asymptotics for {a~Keldysh} pencil},
     journal = {Sbornik. Mathematics},
     pages = {389--404},
     publisher = {mathdoc},
     volume = {51},
     number = {2},
     year = {1985},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1985_51_2_a4/}
}