  For two points in the closure of a simple polygon $P$, we say that they see
each other in $P$ if the line segment uniting them does not intersect the
exterior of $P$. The visibility graph of $P$ is the graph whose vertex set is
the vertex set of $P$ and two vertices are joined by an edge if they see each
other in $P$.
  The characterization of visibility graphs has been an open problem for
decades, and a significant effort has been made to characterize visibility
graphs of restricted polygon classes. Among them is the convex fan: a simple
polygon with a convex vertex (i.e. whose internal angle in less than 180
degrees) that sees every other point in the closure of the polygon (often
called kernel vertex). We show that visibility graphs of convex fans are
equivalent to visibility graphs of terrains with the addition of a universal
vertex, that is, a vertex that is adjacent to every other vertex.
