Special Point Sets in Finite Projective Planes

ing sets, that is blocking sets not containing a proper subset that is still a blocking set. The smallest possible blocking set is always a line. The most interesting problem is the next possible size. Essentially the problem is due to Richardson [15] who considered the plane of order 3, although already in [11] it is mentioned that the only minimal blocking sets in the Fano plane PG(2; 2) are the lines. In PG(2; 3) the next possible size is 6. The problem was made popular by di Paola [12] who determined the next possible size in the planes of order 4, 5, 7, 8 and 9 (answers: 7, 9, 12, 13 and 13). The most general result for the size of a blocking set in arbitrary (not necessarily Desarguesian) projective planes is Bruen's result [8] A minimal blocking set B in a projective plane of order n is either a line, or contains at least<F44