Zaviyalov О. I.; Polivanov М. K. R-operation of Bogolyubov—Parasyuk and operator expansions in mass-free theories . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 44, n. 3, p. 333–340, 1992. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8102. Acesso em: 7 apr. 2025.