ILMAN, V. M. PROPERTIES OF FORMAL STRUCTURES AND SUBSTRUCTURES. Science and Transport Progress , [S. l.], n. 14, p. 99–104, 2007. DOI: 10.15802/stp2007/17863. Disponível em: https://stp.ust.edu.ua/article/view/17863. Acesso em: 9 apr. 2025.