@article{MM2_1980__31_154709,
     author = {D. Happel and U. Preiser},
     title = {Binary {Polyhedral} {Groups} and {Euclidean} {Diagrams.}},
     journal = {Manuscripta mathematica},
     pages = {317--330},
     publisher = {mathdoc},
     volume = {31},
     year = {1980},
     zbl = {0436.20005},
     url = {http://geodesic.mathdoc.fr/item/MM2_1980__31_154709/}
}