Hoxha I, Braha NL.  Weyl's theorem, tensor product, Fuglede-Putnam theorem and continuity spectrum for $k$-quasi class $\mathcal{A}^{*}_{n}$ operators.  J. Korean Math. Soc. 2014;51:1089-1104.  https://doi.org/10.4134/JKMS.2014.51.5.1089