1. A commutativity problem for normal operators;Fuglede,1950
2. Normality can be relaxed in the asymptotic Fuglede-Putnam theorem;Furma,1980
3. On operator commutators;Kleinecke,1957
4. An asymptotic Fuglede theorem;Moore,1975
5. On normal operators on Hilbert space;Putnam;American J. Math.,1951