@book{19313,
	author = {Bridson, Martin R. and Haefliger, Andre and Haefliger, Andre ; jt. auth.},
	title = {Metric spaces of non-positive curvature},
	publisher = {Springer-Verlag},
	year = {1999},
	series = {Grundlehren der Mathematischen Wissenschaften },
	address = {Berlin}
}