On a nonlinear eigenvalue problem for generalized Laplacian in Orlicz-Sobolev spaces

We consider a nonlinear eigenvalue problem for some elliptic equations governed by general operators including the $p$-Laplacian. The natural framework in which we consider such equations is that of Orlicz-Sobolev spaces. we exhibit two positive constants $\lambda_{0}$ and $\lambda_{1}$ with $\lambda_{0}\leq\lambda_{1}$ such that $\lambda_1$ is an eigenvalue of the problem while any value $\lambda<\lambda_{0}$ cannot be so. By means of Harnack-type inequalities and a strong maximum principle, we prove the isolation of $\lambda_{1}$ on the right side. We emphasize that throughout the paper no $\Delta_2$-condition is needed.