Wallpaper Groups
Symmetry group 8  (pgg)
This group contains no reflections, but it has glide-reflections and half-turns.  There are perpendicular axes for the glide-reflections, and the 
fixed points of the half-turns do not lie on these axes.  Again, the lattice is rectangular, and a quarter-rectangle of a fundamental region for the translation group is a fundamental region for the symmetry group..
 In the image on the right, the fixed points of the half-turns are indicated by black dots, and the axes of the glide-reflections are drawn in green.
In the image on the right, the fixed points of the half-turns are indicated by black dots, and the axes of the glide-reflections are drawn in green.
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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/