摘要：In the case of not requiring the nonlinear term to be monotone or convex, we study the existence of positive solutions for second-order periodic boundary value problem by using the first eigenvalue of the corresponding lin- ear problem and fixed point index theory. The work significantly improves and generalizes the main results of J. Graef et al. [A periodic boundary value prob- lem with vanishing Green’s function, Appl. Math. Lett. 21(2008) 176−180].
