M. Gionfriddo, S. Milici and Zs. Tuza, Blocking sets in SQS(2v), Combin. Probab. Comput. 3, 77-86, 1994.
August 14, 1997. Tommy R. Jensen
Zs. Tuza, Inequalities for minimal covering sets in set systems of given rank, Discrete Appl. Math. 51, 187-195, 1994.
August 27, 1997. Tommy R. Jensen