@article{1102978251, author = {Headley, V. B.}, title = {A monotonicity principle for eigenvalues.}, journal = {Pacific J. Math.}, volume = {31}, number = {3}, year = {1969}, pages = { 663-668}, language = {en}, url = {http://dml.mathdoc.fr/item/1102978251} }
Headley, V. B. A monotonicity principle for eigenvalues.. Pacific J. Math., Tome 31 (1969) no. 3, pp. 663-668. http://gdmltest.u-ga.fr/item/1102978251/