ZAGORODNYUK, S. M. Positive definite kernels satisfying difference equations. Methods of Functional Analysis and Topology, [S. l.], v. 16, n. 1, p. 83–100, 2010. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/442. Acesso em: 16 dec. 2025.