Stability of some essential B-spectra of pencil operators and application. Extracta Mathematicae, [S. l.], v. 36, n. 1, p. 63–80, 2021. DOI: 10.17398/2605-5686.36.1.63. Disponível em: https://revista-em.unex.es/index.php/EM/article/view/2605-5686.36.1.63.. Acesso em: 21 dec. 2024.