Hierarchy classification:

1. top of the aat hierarchies
2. Associated Concepts Facet
3. Associated Concepts (hierarchy name)
4. scientific concepts
5. mathematical concepts
6. geometric concepts
7. geometric figures
8. plane figures
9. polygons

Anotations

Scope note:

Polygons having one edge and one vertex, considered an impossible object in Euclidean geometry. In spherical geometry, a finite henagon may be drawn by placing a single vertex anywhere on a great circle; two henagons may be used to construct a dihedron on a sphere.