AN EXTENSION OF THE FUGLEDE-PUTNAM THEOREM TO k-QUASIHYPONORMAL OPERATORS

The Fulgede-Putnam theorem asserts as if A and Bare normal operators and X is an operator such that AX=XB, then A*X=XB*. In this paper, we show that if A is k-quasihyponormal and B* is invertible k-quasihyponormal such that AX=XB for a Hilbert-Schmidt operator X, then A*X=XB*.