Which rotations occur in a frieze group?Is it possible to draw a frieze pattern which has a vertical axis of reflection and a horizontal axis of reflection, but has no rotational symmetry (apart from the rotation through the angle of zero!)? If yes, then draw such a pattern. If not, then explain why not.

Maybe you can look here for some help
Frieze group - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Frieze_group)