POPOVYCH, S. V. Algebraically admissible cones in free products of $*$-algebras. Methods of Functional Analysis and Topology, [S. l.], v. 16, n. 1, p. 51–56, 2010. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/439. Acesso em: 16 dec. 2025.