1. Aiena, P.: Fredholm and local spectral theory with applications to multipliers. Kluwer Academic Publishers, Dordrecht (2004)
2. Álvarez, T.: Perturbation theorems for upper and lower semi-Fredholm linear relations. Publ. Math. Debrecen. 65(1–2), 179–191 (2004)
3. Álvarez, T.: On regular linear relations. Acta Math. Sinica (English Ser.) 28(1), 183–194 (2012)
4. Álvarez, T.: Small perturbation of normally solvable relations. Publ. Math. Debrecen. 80(1–2), 155–168 (2012)
5. Álvarez, T., Ammar, A., Jeribi, A.: On the essential spectra of some matrix of linear relations. Math. Methods Appl. Sci. 37(5), 620–644 (2014)