@article{TMF_2013_177_2_a1,
     author = {A. B. Shabat},
     title = {Periodic solutions of {the~Hopf} equation},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {222--230},
     publisher = {mathdoc},
     volume = {177},
     number = {2},
     year = {2013},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_2013_177_2_a1/}
}