POPOVYCH, D. A contraction between Lie algebras with necessarily singular components of the contraction matrix . Reports of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, n. 7, p. 29–35, 2014. DOI: 10.15407/dopovidi2014.07.029. Disponível em: https://nasu-periodicals.org.ua/index.php/dp/article/view/16578. Acesso em: 20 jun. 2026.