Variational Methods for Nonlinear Elliptic Eigenvalue Problems Paul Rabinowitz Indiana University Mathematics Journal 1974 text pdf 10.1512/iumj.1974.23.23061 10.1512/iumj.1974.23.23061 en Indiana Univ. Math. J. 23 (1974) 729 - 754 state-of-the-art mathematics http://iumj.org/access/