We develop a structure theory for near polygons with quads. Main results are the existence of sub 2j-gons for 2 ~ 4 with s > 1 and t 2 > 1 and t 3 5 ~ t2(t 2 + 1).

No abstract

No abstract

No abstract

Using theorems of Redei, and of Brouwer and Schrijver, and Jamison, it is proved that a non-trivial blocking set in a desarguesian projective plane of order q has at least q + v (2q) + I points, if q is at least 7. odd and not a square and q i' 27. Further one can show that non-trivial blocking sets in the desarguesian planes PG(2, 11) and PG(2, 13) have at least 18 resp. 21 points, and this is best possible. In addition a nice description of a blocking set of size qt +qt-1 +I in the desarguesian plane PG(2, q') is given, where q is some prime power.