Rotation symmetry? 
Cambridge 
 - Cambridge  Cambridge University Press  1993 
 - 8 p. : ill 
<br/><br/><label>ISBN: </label>9780521439459 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Maths
<br/><br/><label>Dewey Class. No.: </label>510 CAM