MAO, Lixin; ZHU, Haiyan. Relative Extensions of Modules and Homology Groups. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 67, n. 9, p. 1232–1243, 2015. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2061. Acesso em: 5 dec. 2025.