Ameera Chowdhury Chris D. Godsil Gordon F. Royle Colouring lines in projective space. 39-52 2006 113 J. Comb. Theory, Ser. A 1 http://dx.doi.org/10.1016/j.jcta.2005.01.010 db/journals/jct/jcta113.html#ChowdhuryGR06