POPOV, T.P. New singular solutions for the (3+1)-D Protter problem. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 91, n. 3, p. 61–68, 2018. DOI: 10.31489/2018m3/61-68. Disponível em: https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/265. Acesso em: 10 jul. 2025.