1. Bishop, R., Crittenden, R.: Geometry of Manifolds. Academic Press, New York, London, 1964
2. Cheeger, J.: Spectral Geometry of Spaces with Cone-Like Singularities. Preprint
3. Chernoff, P.: Essential Self Adjointness of Powers of Generators of Hyperbolic Equations. J. Functional Analysis. 12, 401–414 (1973)
4. Coddington, E., Levinson, N.: Theory of Ordinary Differential Equations. Mc-Graw Hill, New York, Toronto, London, 1955
5. Dodziuk, J.: L2 Harmonic Forms on Rotationally Symmetric Riemannian Manifolds. Proc. Amer. Math. Soc.77, 395–400 (1979)