设H是复数域C上的Hilbert空间且dimH≥2,Bs(H)是H上所有自伴算子全体。设Φ是Bs(H)上的双射,如果Φ满足对任意A,B∈Bs(H),都有‖Φ(A)Φ(B)+Φ(B)Φ(A)‖=‖AB+BA‖,则存在一个酉算子或反酉算子U和泛函h:B(H)→{1,-1}使得对任意X∈B(H),有Φ(X)=h(X)UXU*。
Let H be a complex Hilbert space with dimH≥2 and let Bs(H) be the space of all self-adjoint operators on H.Let Φ be a bijective map on Bs(H).It is proved that if ‖Φ(A)Φ(B)+Φ(B)Φ(A)‖=‖AB+BA‖ for all A,B∈Bs(H),then there is a unitary operator or a conjugate unitary operator U and a functional h from Bs(H) to {1,-1} such that Φ(X)=h(X)UXU for all X∈Bs(H).