1. R.P. Agarwal, M. Bohner, P.J.Y. Wong, Positive solutions and eigenvalues of conjugate boundary value problems. Proc. Edinb. Math. Soc. (Ser. 2) 42, 349–374 (1999)
2. R.P. Agarwal, S.R. Grace, D. O’Regan, Existence of positive solutions to semipositone Fredholm integral equations. Funkcial. Ekvac. 45, 223–235 (2002)
3. R.P. Agarwal, J. Henderson, P.J.Y. Wong, On superlinear and sublinear (n, p) boundary value problems for higher order difference equations. Nonlinear World 4, 101–115 (1997)
4. R.P. Agarwal, M. Meehan, D. O’Regan, Nonlinear Integral Equations and Inclusions (Nova Science Publishers, Hungtington, 2001)
5. R.P. Agarwal, M. Meehan, D. O’Regan, Positive solutions of singular integral equations—a survey. Dyn. Syst. Appl. 14, 1–37 (2005)