@article{IVM_1980_9_a11,
     author = {R. P. Shepeleva},
     title = {Critical frequencies of canonical systems, invariant with respect to time reversal, with periodic coefficients},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {56--64},
     publisher = {mathdoc},
     number = {9},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1980_9_a11/}
}