1. Positive Solutions of Operator Equations;Krasnosel'skii,1964
2. On a type of nonlinear integral equation;Urysohn;Siberian Math. J.,1924
3. Maximum Principles in Differential Equations;Protter,1967
4. Nonexistence and uniqueness of positive solutions of nonlinear eigenvalue problems;Keller;Bull. Amer. Math. Soc.,1968
5. Positive solutions of some nonlinear eigenvalue problems;Keller;J. Math. Mech.,1969