Let Λ and Γ be Artin algebras, M a Γ-Λ-bimodule, and R the triangular matrix ring of Λ, Γ, and M; assume that R is also an Artin algebra. The R-modules are triples (U, V, f) where U is a Λ-module, V ...

Abstract. The spectra of the 2 × 2 upper triangular operator matrix M C =( A C 0 B ) acting on a Hilbert space 𝐻₁ ⨁ 𝐻₂ are investigated. We obtain a necessary and sufficient condition of 𝜎(𝑀𝐶) = ...