@article{RM_1981_36_1_a5,
     author = {H. Zieschang},
     title = {On decompositions of discrete groups of motions of the plane},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {193--215},
     publisher = {mathdoc},
     volume = {36},
     number = {1},
     year = {1981},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1981_36_1_a5/}
}