HOY, E. Area theorems and Fredholm eigenvalues. Annales Fennici Mathematici, [S. l.], v. 14, n. 1, p. 137–148, 1989. DOI: 10.5186/aasfm.1989.1412. Disponível em: https://afm.journal.fi/article/view/134653. Acesso em: 25 nov. 2024.