# Wallpaper Groups

### Symmetry group 9 (cmm)

This group has perpendicular reflection axes, as does group 6 (pmm), and has half-turns, that is, rotations of order 2. Some of the centers of the the half-turns lie on the intersections of the axes of reflection, but others lie on the intersections of the axes of the glide reflections. The lattice is rhomic, and a quarter of a fundamental region for the translation group is a fundamental region for the symmetry group.

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© 1994, 1997.

David E. Joyce

Department of Mathematics and Computer Science

Clark University

Worcester, MA 01610

These files are located at http://aleph0.clarku.edu/~djoyce/wallpaper/