摘要
Yang Liming showed in 1988 that if S is a subnormal operator, T is a hyponormal operator and T and S are quasisimilar, then σ_e(S)(?) σ_e(T), and hence he deduced the conclusion that two quasisimilar subnormal operators have equal essential spectra. This is an important result in the theory of quasisimilarity. In this note we improve Yang’s method to show that if S or S is subnormal, T is a bounded linear operator and T and S are quasisimilar, then σ_e(S) (?) σ_e(T).
基金
Project supported by the Science Foundation of Fujian Province
