Aart Blokhuis Ruud Pellikaan Tamás Szonyi Blocking Sets of Almost Rédei Type. 141-150 1997 78 J. Comb. Theory, Ser. A 1 http://dx.doi.org/10.1006/jcta.1996.2736 db/journals/jct/jcta78.html#BlokhuisPS97