Existence theorems for a class of nonlocal differential equations

A class of nonlocal second-order ordinary differential equations of the form y (x) = f x, y(x), (y ◦ λ)(x), y (x) for continuous f and λ is studied. The equation is supplemented with none, one, or two Robin boundary conditions depending on whether the interval of interest I is finite, semi-infinite or infinite. The only other restriction on the function λ is that it maps I into itself. Sufficient conditions for the existence of a solution are found, which include the assumption of the existence of ‘upper’ and ‘lower’ solutions. The upper and lower solutions provide bounds for the solution on I . © 2005 Elsevier Inc. All rights reserved.