 
Summary: EuroCG 2010, Dortmund, Germany, March 2224, 2010
Blocking Coloured Point Sets
Greg Aloupis
Brad Ballinger
S´ebastien Collette§
Stefan Langerman¶
Attila P´or
David R. Wood
1 Introduction
This paper studies problems related to visibility and
blocking in sets of coloured points in the plane. A
point x blocks two points v and w if x is in the in
terior of the line segment vw. Let P be a finite set
of points in the plane. Two points v and w are vis
ible with respect to P if no point in P blocks v and
w. The visibility graph of P has vertex set P, where
two distinct points v, w P are adjacent if and only
if they are visible with respect to P. A point set B
blocks P if P B = and for all distinct v, w P
there is a point in B that blocks v and w. That is, no
