Creating images by adding masses to gravitational point lenses
  A well-studied maximal gravitational point lens construction of S. H. Rhie
produces $5n$ images of a light source using $n+1$ deflector masses. The
construction arises from a circular, symmetric deflector configuration on $n$
masses (producing only $3n+1$ images) by adding a tiny mass in the center of
the other mass positions (and reducing all the other masses a little bit).
  In a recent paper we studied this "image creating effect" from a purely
mathematical point of view (S\`ete, Luce & Liesen, Comput. Methods Funct.
Theory 15(1):9-35, 2015). Here we discuss a few consequences of our findings
for gravitational microlensing models. We present a complete characterization
of the effect of adding small masses to these point lens models, with respect
to the number of images. In particular, we give several examples of maximal
lensing models that are different from Rhie's construction and that do not
share its highly symmetric appearance. We give generally applicable conditions
that allow the construction of maximal point lenses on $n+1$ masses from
maximal lenses on $n$ masses.
