Remarks on multiplicity of solutions for a subquadratic elliptic equation

We consider a subquadratic elliptic equation in a bounded domain Ω⊂R^N$\Omega \subset {\mathbb{R}}^N$ (N?1$N?1$). By the Clark Theorem, we obtain the existence and multiplicity of its nontrivial solutions, and we show that this result has a great relationship with Ω itself. The above argument can be extended to biharmonic equations.