The existence of positive solution of systems of Volterra nonlinear difference equations. Neliniini Kolyvannya, [S. l.], v. 9, n. 1, p. 37–47, 2006. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/377. Acesso em: 22 jan. 2026.