Zoltán Füredi Dhruv Mubayi Oleg Pikhurko Quadruple systems with independent neighborhoods. 1552-1560 2008 115 J. Comb. Theory, Ser. A 8 http://dx.doi.org/10.1016/j.jcta.2008.01.008 db/journals/jct/jcta115.html#FurediMP08