YAACOB, Yusof. Penyelesaian Berkala Persamaan Pembeza York. MATEMATIKA, [S. l.], v. 7, p. 1–9, 1991. DOI: 10.11113/matematika.v7.n.457. Disponível em: https://matematika.utm.my/index.php/matematika/article/view/457. Acesso em: 5 may. 2024.