1. Aiena P.: Fredholm and Local Spectral Theory, with Applications to Multipliers. Kluwer Academic Publishers, USA (2004)
2. Aiena P., Mbekhta M.: Characterization of some classes of operators by means of the Kato decomposition. Boll. Un. Mat. Ital. VII. Ser. A 10(3), 609–621 (1996)
3. Álvarez T.: On regular linear relations. Acta Math. Sinica (English Ser.) 28(2), 183–194 (2012)
4. Baskakov A.G., Chernyshov K.I.: Spectral analysis of linear relations, and degenerate semigroups of operators. Sb. Math. 193, 1573–1610 (2002)
5. Benharrat M., Messirdi B.: Relationship between the Kato essential spectrum and a variant of essential spectrum. Gen. Math. 20(4), 71–88 (2012)