Benharrat, MOHAMMED; Messirdi, BEKKAI
(Univ. Oradea Fasc. Mat. XXI (1), 2014)
J. P. Labrousse [13] studied and characterized in the case of Hilbert spaces, a
relation of the essential quasi-Fredholm spectrum and the spectrum de ned by Goldberg
in [9] by ec(A) = f 2 C ; R( I A) is not closedg. ...