P S p 4 (3) as a symmetric (36, 15, 6)-design Dieter Held, Jörg Hrabě De Angelis, Mario-Osvin Pavčević (1999) Rendiconti del Seminario Matematico della Università di Padova
Packing graphs: The packing problem solved. Caro, Yair, Yuster, Raphael (1997) The Electronic Journal of Combinatorics [electronic only]