KRALL, H. L.; SHEFFER, I. M. On Trigonometric Polynomials Satisfying Differential Equations. The Journal of the Indian Mathematical Society, [S. l.], v. 39, n. 1-4, p. 29–49, 1975. Disponível em: http://informaticsjournals.com/index.php/jims/article/view/16635. Acesso em: 5 may. 2024.