# visibility graph

## Obstacle number of planar graphs ★

Author(s): Alpert; Koch; Laison

Does there exist a planar graph with obstacle number greater than 1? Is there some $k$ such that every planar graph has obstacle number at most $k$?

## Point sets with no empty pentagon ★

Author(s): Wood

\begin{problem} Classify the point sets with no empty pentagon. \end{problem}

Keywords: combinatorial geometry; visibility graph