Template:Gromoll&Wolf1971
From Manifold Atlas
D. Gromoll and J. A. Wolf, Some relations between the metric structure and the algebraic structure of the fundamental group in manifolds of nonpositive curvature, Bull. Amer. Math. Soc. 77 (1971), 545–552. MR0281122 (43 #6841) Zbl 0237.53037
