Estimates for the Bounds of the Essential Spectrum of a 2 × 2 Operator Matrix. Contemporary Mathematics , [S. l.], v. 1, n. 4, p. 170–186, 2020. DOI: 10.37256/cm.142020409. Disponível em: https://ojs353.mebyme.cn/index.php/CM/article/view/409. Acesso em: 24 dec. 2025.