@article{DAN_1968_178_4_a2,
     author = {A. B. Vasil'eva and V. A. Tupchiev},
     title = {Periodic solutions of systems of differential equations with a small parameter at the derivatives, close to discontinuous ones},
     journal = {Doklady Akademii Nauk},
     pages = {767--770},
     publisher = {mathdoc},
     volume = {178},
     number = {4},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_178_4_a2/}
}