[1]
Karmouni, M., Tajmouati, A. and A. El Bakkali, A. 2019. Upper triangular operator matrices and limit points of the essential spectrum. Proyecciones (Antofagasta, On line). 38, 3 (Aug. 2019), 401-409. DOI:https://doi.org/10.22199/issn.0717-6279-2019-03-0026.