摘要
LET H be an infinite-dimensional complex Hilbert space with inner product 【·,·】 and B(H) the von Neumann algebra of all bounded linear operators on H. For T∈B(H), σ(T), as usual, will denote the spectrum of T. Let Φ be a linear map from B(H) into itself. Φ is spectrum-preserving if σ(Φ(T))=σ(T) for all T∈B(H); Φ is spectrum-compressing
