@article{MM2_1988__60_2_155294,
     author = {Eng Tjioe Tan},
     title = {Remarks on free {Bieberbach} {Groups.}},
     journal = {Manuscripta mathematica},
     pages = {477--486},
     publisher = {mathdoc},
     volume = {60},
     number = {2},
     year = {1988},
     zbl = {0654.20059},
     url = {http://geodesic.mathdoc.fr/item/MM2_1988__60_2_155294/}
}