KOPYLOV, Yaroslav. On the Lambek Invariants of Commutative Squares in a Quasi-Abelian Category. Scientia Series A: Mathematical Sciences, [S. l.], v. 11, p. 57–67, 2005. DOI: 10.71712/. Disponível em: https://revistas.usm.cl/scientia/article/view/73.. Acesso em: 7 jun. 2025.