压缩算子与等距算子的拟相似

Quasisimilarity between Contractions and Isometries

本文给出了压缩算子与酉算子（非酉等距算子）拟相似有相同本质谱的充要条件，并且证明了亚正常算子与等距算子如果稠相似必有相同的本质谱。

This paper gives necessary and sufficient condition for quasisimilar contraction and isometry(unitary operator)to have equal essential spectra.It gives also an elementary proof of the equality of essential spectra of densely similar hyponormal operator and isometry.