Aart Blokhuis: Reducing the discrete diameter of a point set.
By the discrete diameter of a point set in a finite projective
or affine plane we mean the maximum of the size of the intersection
of a line with this set. The question we then want to answer is:
How many points does one have to remove to reduce the diameter
of the point set?
The point set we look at in the talk is the union of a number of
Baer subplanes of a projective plane.