Blocking-sets contenuti nell’unione di tre rette formanti fascio

Abstract

Let $PG(2,q)$ be the Galois plane of order q and let $n(q)$ be the minimum integer such that there exists a $n(q)$ blocking-set of $PG(2,q)$ contained in the union of three lines which pass through the same point.In this paper we prove that, if q is odd, $n(q)≥ \frac{3q+5}{2}$ and we give an example of minimal blocking-set in $PG(2,9)$.