@article{UFA_2011_3_2_a2,
     author = {V. V. Yevstafyeva},
     title = {On necessary conditions for existence of periodic solutions in a~dynamic system with discontinuous nonlinearity and an external periodic influence},
     journal = {Ufa mathematical journal},
     pages = {19--26},
     publisher = {mathdoc},
     volume = {3},
     number = {2},
     year = {2011},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/UFA_2011_3_2_a2/}
}