1. Positive Solutions of Operators Equations;Krasnoselskii,1964
2. Nonlinear Functional Analysis;Deimling,1985
3. Nonlinear Problem in Abstract Cones;Guo,1988
4. Periodic solutions of single-species models with periodic delay;Freedman;SIAM J. Math. Anal.,1992
5. Theory of Functional Differential Equations;Hale,1977