# 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 such that every planar graph has obstacle number at most ?

Keywords: graph drawing; obstacle number; planar graph; visibility graph

## Point sets with no empty pentagon ★

Author(s): Wood

**Problem**Classify the point sets with no empty pentagon.

Keywords: combinatorial geometry; visibility graph