@book{14423,
	author = {Lydon, Roger C. and Schupp, Paul E. and Schupp, Paul E.},
	title = {Combinatorial group theory},
	publisher = {Springer-Verlag},
	year = {1977},
	series = {Ergebnisse der mathematik und ihrer Grezgebiete},
	address = {Berlin}
}