ISSN : 1226-0657
Let H be an arbitrary complex Hilbert space and let (equation omitted)(H) be the *-algebra of all bounded linear operators on H. An operator T in (equation omitted)(H) is called normal if T<TEX>$\^$</TEX>*/T = TT<TEX>$\^$</TEX>*/, hyponormal if T<TEX>$\^$</TEX>*/T <TEX>$\geq$</TEX> TT<TEX>$\^$</TEX>*/, and quasi-hyponormal if T<TEX>$\^$</TEX>*/(T<TEX>$\^$</TEX>*/T - TT<TEX>$\^$</TEX>*/)A <TEX>$\geq$</TEX> 0, or equivalently ∥T<TEX>$\^$</TEX>*/T<TEX>$\chi$</TEX>∥ <TEX>$\leq$</TEX> ∥TT<TEX>$\chi$</TEX>∥ for all <TEX>$\chi$</TEX> in H.(omitted)