SORJONEN, P. Extensions of isometric and symmetric linear relations in a Krein space. Annales Fennici Mathematici, [S. l.], v. 5, n. 2, p. 355–375, 1980. DOI: 10.5186/aasfm.1980.0524. Disponível em: https://afm.journal.fi/article/view/134392. Acesso em: 25 nov. 2024.