@article{RM_1976_31_5_a17,
     author = {H. Zieschang},
     title = {On~triangle groups},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {226--233},
     publisher = {mathdoc},
     volume = {31},
     number = {5},
     year = {1976},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1976_31_5_a17/}
}