@article{INTG_1991_23_a3,
     author = {\`E. G. Poznyak and A. G. Popov},
     title = {Geometry of the {sine-Gordon} equation},
     journal = {Itogi Nauki i Tekhniki. Seriya Problemy Geometrii. Trudy Geometricheskogo Seminara},
     pages = {99--130},
     year = {1991},
     volume = {23},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTG_1991_23_a3/}
}