HORADAM, A. F.; SHANNON, A. G. Ward’s Staut-Clausen problem. MATHEMATICA SCANDINAVICA, [S. l.], v. 39, p. 239–250, 1976. DOI: 10.7146/math.scand.a-11659. Disponível em: https://www.mscand.dk/article/view/11659. Acesso em: 3 may. 2024.