KANDAGURA, A. N.; ASHUROVA, E. N.; KARPENKO, I. I. A simplicity criterion for symmetric operator on a graph. Methods of Functional Analysis and Topology, [S. l.], v. 20, n. 2, p. 117–123, 2014. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/572. Acesso em: 15 dec. 2025.