Some results on Fredholmness and boundedness below of an upper triangular operator matrix

In this paper, for given operators A∈B(H)A∈B(H) and B∈B(K)B∈B(K), we completely describe the set of all C∈B(K,H)C∈B(K,H) such that MCMC is bounded below, left (right) semi-Fredholm, respectively.