PILCHAK, B. Yu. Об исчислении задач. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 4, n. 2, p. 174–195, 1952. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/6638. Acesso em: 6 dec. 2025.