@book{21702,
	author = {Ballmann, Werner},
	title = {Lectures on spaces of nonpositive curvature},
	publisher = {Birkhauser Verlag},
	year = {1995},
	series = {DMV Seminar band },
	address = {Basel},
	note = {With an appendix by Misha Brin Ergodicity of Geodesic Flows}
}