Blocking sets in designs with block size four. II (Q1175420)

The authors establish the existence of block designs on \(n\) points with block size 4 that admit a blocking set for all \(n\equiv 0\) or 1 (mod 4) if \(\lambda=3\), and for all \(n\geq 4\) if \(\lambda=6\) (repeated blocks are allowed). Group divisible designs are used in their constructions. Coupled with results from their earlier paper, which appeared in the Eur. J. Comb. 11, No. 5, 451-457 (1990), they now have, except for a few cases, a complete solution to the existence question of block designs with block size 4 that admit a blocking set.