1. Perturbation of eigenvalues—with an engineering application;Birnbaum;SIAM Rev.,1965
2. Vibration problems in engineering;Timoshenko,1955
3. On the upper and lower bounds of eigenvalues;Kato;J. Phys. Soc. Japan,1949
4. Quadratic forms in Hilbert spaces and asymptotic perturbation series;Kato,1955
5. Équations Différentielles Opérationelles et Problèmes aux Limites;Lions,1961