An Upper and Lower Solution Theory for the Problem (G'(y))' + f(t, y) = 0 on Finite and Infinite Intervals.

A new upper and lower solution theory is presented for the second order problem (G'(y))' + f(t, y) = 0 on finite and infinite intervals. The theory on finite intervals is based on a Leray-Schauder alternative, whereas the theory on infinite intervals is based on results on the finite interval and a diagonalization process. [ABSTRACT FROM AUTHOR]