@article{GDZPPN002425416, title = {Aspherical Group Presentations.}, journal = {Mathematische Zeitschrift}, volume = {177}, year = {1981}, pages = {1-36}, zbl = {0443.20030}, url = {http://dml.mathdoc.fr/item/GDZPPN002425416} }
Collins, Donald J.; Chiswell, Ian M. Aspherical Group Presentations.. Mathematische Zeitschrift, Tome 177 (1981) pp. 1-36. http://gdmltest.u-ga.fr/item/GDZPPN002425416/