1. Fuzzy sets;Zadeh;Inform. Control,1965
2. Outline of fuzzy set theory;Dubois,1979
3. A fuzzy symmetry concept for forms with imperfect symmetries;Köhler;Computers Math. Applic.,1991
4. Description of forms and form transitions;Köhler,1988
5. Symmetrien von Ornamenten und Kristallen;Klemm,1982