English: Symmetries of a regular enneagon, with markups
Reworked from "The Symmetries of Things", Chapter 20
The regular enneagon has Dih9 dihedral symmetry, order 18, and 5 lower dihedral and cyclic symmetries. The dihedral symmetries pass through vertices and edges. Cyclic symmetries in the middle column are labeled as g for their central gyration orders.