1. Akhiezer, N.: The Classical Moment Problem. Hafner, New York (1965)
2. Aizenman, M., Simon, B.: Brownian motion and Harnack’s inequalities for Schrödinger operators. Comm. Pure Appl. Math. 35, 209–273 (1982)
3. Burchard, A., Schmuckenschläger, M.: Comparison theorems for exit times. GAFA 11, 651–692 (2002)
4. Chavel, I.: Eigenvalues in Riemannian Geometry. Academic Press, New York (1984)
5. Gilkey, P.B.: Asymptotic Formulae in Spectral Geometry. Chapman Hall CRC, Boca Raton (2004)