PageHeader : Funkcialaj Ekvacioj, 34 (1991) 287-302 Title : Representation Formula for Cluster Sets of Eigenvalues AuthorInfo : By AuthorInfo : Masafumi YOSHINO AuthorInfo : (Chuo University, Japan) AuthorInfo : Dedicated to Prof. Niro Yanagihara for his 60th birthday section : 1. Introduction section : 2. Operators in the complex domain section : 3. Proof of theorems section : 4. Operators on the torus section : 5. Inverse problems and the stability of $C(P)$ subsection : 5.2. Properties of $F_{\sigma}(t)$ and $\tilde{F}_{\sigma}(t)$ . subsection : 5.3. Proof of Theorem 5.2. section : 6. Operators with non-proper $\Gamma(P)$ section : 7. Applications section : References