1. Variational Methods in Eigenvalue Problems;Gould,1957
2. Ordinary Differential Equations;Ince,1944
3. “Some Results on the Frequencies of Nonhomogeneous Rods,”;Schwarz;J. Math. Anal. Appl.,1962
4. Bounds for the Principal Frequency of Nonuniformly Loaded Strings;Schwarz,1962
5. “On Certain Problems on the Maximum and Minimum of Characteristic Values and on the Lyapunov Zones of Stability,”;Krein;Amer. Math. Soc. Translations, Series 2,1955