FRIEDMAN, M.; TEICHER, M. On fundamental groups related to degeneratable surfaces: conjectures and examples. ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE, [S. l.], v. 11, n. 3, p. 565-603, 2012. DOI: 10.2422/2036-2145.201002_005. Disponível em: https://journals.sns.it/index.php/annaliscienze/article/view/276. Acesso em: 20 feb. 2026.