@article{IVM_2015_8_a1,
     author = {E. V. Derunova and Yu. I. Sapronov},
     title = {Application of normalized key functions in a~problem of branching of periodic extremals},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {14--24},
     publisher = {mathdoc},
     number = {8},
     year = {2015},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_2015_8_a1/}
}