@inbook{10.2307/j.ctt155jm66.6,
 ISBN = {9780691080451},
 URL = {http://www.jstor.org/stable/j.ctt155jm66.6},
 abstract = {This lecture will have a more systematic character than the preceding one, in as much as it will be dedicated to one special kind of geometric symmetry, the most complicated but also the most interesting from every angle. In two dimensions the art of surface ornaments deals with it, in three dimensions it characterizes the arrangement of atoms in a crystal. We shall therefore call it the ornamental or crystallographic symmetry.Let us begin with an ornamental pattern in two dimensions which probably occurs more frequently than any other, both in art and nature: the hexagonal pattern so often used},
 bookauthor = {HERMANN WEYL},
 booktitle = {Symmetry},
 pages = {83--116},
 publisher = {Princeton University Press},
 title = {ORNAMENTAL SYMMETRY},
 year = {1980}
}