Fredholm Operator Matrices Under Demicompactness
Bilel Krichen · 2025
In this chapter, we will study the demicompactness properties of https://www.w3.org/1998/Math/MathML" display="inline"> 2 × 2 operator matrices acting on a product of Banach spaces product. In general, the entries of https://www.w3.org/1998/Math/MathML" display="inline"> L 0 are unbounded. We first start by providing sufficient conditions on the entries of the matrix operator https://www.w3.org/1998/Math/MathML" display="inline"> L 0 to be closable and its closure is given. Then we investigate the essential spectrum of the closure involving the demicompactness class.