Rashid, M. H. M., and M. S. M. Noorani. 2009. “On Relaxation Normality in the Fuglede-Putnam Theorem for a Quasi-Class $A$ Operators”. Tamkang Journal of Mathematics 40 (3):307-12. https://doi.org/10.5556/j.tkjm.40.2009.508.