The Eigenvalue Problem for Sublinear Hammerstein Operators with Oscillation Kernels George Pimbley, Jr. Indiana University Mathematics Journal 1963 text pdf 10.1512/iumj.1963.12.12037 10.1512/iumj.1963.12.12037 en Indiana Univ. Math. J. 12 (1963) 577 - 597 state-of-the-art mathematics http://iumj.org/access/