Solvability of the resonant 1-dimensional periodic p-Laplacian equations

In this paper we study the existence of 2π-periodic solutions of−(|x′|p−2x′)′=λ|x|p−2x+f(t),x∈R where p>1p>1, λ is an eigenvalue of the corresponding homogeneous equation, f is a 2π-periodic function. Some existence results are proved via the Morse theory.