Hyponormal operators and Dunford's condition (B)
It is shown that every cohyponormal operator satisfying a Dunford's condition (B) is necessarily normal; the existence of an invariant subspace for such operators was proved by J. G. Stampfli. On the other hand, it is shown that, in spite of the fact that every subnormal or subspectral operator inherently satisfies condition (B), a hyponormal operator may fail to satisfy that condition.
scientific article; zbMATH DE number 3884811
scientific article