@article{RM_1966_21_3_a8,
     author = {H. Zieschang},
     title = {Discrete groups of plane motions and plane group images},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1966_21_3_a8/}
}