On relative essential spectra of a 3 × 3 operator matrix involving relative generalized weak demicompactness


Imen Ferjani, Aref Jeribi, Bilel Krichen




In this paper, we investigate the relative essential spectra of a 3 × 3 block matrix operator with unbounded entries and with domain consisting of vectors satisfying certain relations between their components. Our results are formulated in term of relative generalized weak demicompactness and measure of non-strict-singularity