GRANNELL M.J.; GRIGGS T.S.; STANTON R.G. On λ-fold coverings with maximum block size four for λ ≥ 6. Utilitas Mathematica , [S. l.], v. 66, 2004. Disponível em: https://utilitasmathematica.com/index.php/Index/article/view/315. Acesso em: 8 may. 2026.