@article{RM_2001_56_5_a5,
     author = {P. G. Grinevich and S. P. Novikov},
     title = {Real finite-zone solutions of the {sine-Gordon} equation: a~formula for the topological charge},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {980--981},
     publisher = {mathdoc},
     volume = {56},
     number = {5},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_2001_56_5_a5/}
}