RUGIRI, Peter Githara. Spectrum of bounded operators in Hilbert spaces . Editon Consortium Journal of Physical and Applied Sciences, [S. l.], v. 3, n. 1, p. 119–123, 2023. DOI: 10.51317/ecjpas.v3i1.411. Disponível em: https://editoncpublishing.org/ecpj/index.php/ecjpas/article/view/411. Acesso em: 19 aug. 2026.