KOREC, Ivan. Additive conditions on sums of squares. Annales Mathematicae Silesianae, [S. l.], v. 12, p. 35–51, 1998. Disponível em: https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/14162. Acesso em: 5 jul. 2025.