1. Le Spectre d'une Variete Riemannienne;Berger;Springer Lecture Notes,1971
2. Geometry of Manifolds;Bishop,1964
3. A Lower Bound for the Smallest Eigenvalue of the Laplacian;Cheeger,1970
4. Eigenvalue Comparison Theorems and its Geometric Applications;Cheng;Math. Z.,1975
5. Spectral Geometry for Certain Noncompact Riemannian Manifolds;Donnelly;Math. Z.,1979