Five Point Mass Gravitational Lenses in a Rhombus as a Soluble Model
  Giving the Maximum Number of Images
  As an extension of four point mass lenses at the vertices of a rhombus, we
present five point mass lenses at the center and vertices of a diamond, which
constitute, for a source behind the center, a soluble model giving expressions
of all the image positions (with the maximum number of images as twenty for
five lenses). For a source near the center, all the image positions are
obtained in the linear approximation.
