1. Auchmuty, G. (1986). Dual variational principles for eigenvalue problems. Proc. Symp. Pure Mathematics, A.M.S., 45:55–72.
2. Auchmuty, G. (1989a). Unconstrained variational principles for eigenvalues of real, symmetric matrices. SIAM J. Math Anal, 20:1186–1207.
3. Auchmuty, G. (1989b). Variational principles for eigenvalues of compact operators. SIAM J. Math Anal, 20:1321–1335.
4. Bandle, C. (1980). Isoperimetric inequlaities and applications. Pitman, London.
5. Belgacem, F. (1997). Elliptic boundary value problems with indefinite weights: variational formulations of the principal eigenvalue and applications. Pitman Research Notes in Mathematics Vol. 368. Longman, Harlow.