摘要
For a hyponormal operator T if there is a polynomial p(·) such that σ(p(T))= {0}, then p(T) =0. In general, it is proved in this way: from σ(p(T)) =0, we know that σ(T) consists of finite points, and therefore T must be normal and so is p(T), hence p(T) =0.
基金
Project supported by the National Natural Science Foundation of China
