Weyl spectra of operator matrices

In this paper it is shown that if $M_{C}=\left (\begin{smallmatrix}A&C\ 0&B\end{smallmatrix}\right )$ is a $2\times 2$ upper triangular operator matrix acting on the Hilbert space $\mathcal{H}\oplus \mathcal{K}$ and if $\omega (\cdot )$ denotes the ``Weyl spectrum", then the passage from $\omega (A)\cup \omega (B)$ to $\omega (M_{C})$ is accomplished by removing certain open subsets of $\omega (A) \cap \omega (B)$ from the former, that is, there is equality where $\mathfrak{S}$ is the union of certain of the holes in $\omega (M_{C})$ which happen to be subsets of $\omega (A)\cap \omega (B)$.