[2] Bezdek J. C.: 
Pattern Recognition with Fuzzy Objective Function Alghorithms. Plenium Press, New York, 1981.  
MR 0631231 
[3] Diday, E, Simon J. C.: Clustering Analysis. In FU K. S. Digital Pattern Recognition, Springer-Verlag, New York (1980), 47–92. 
[4] Dubois D., Prade H.: 
Fuzzy Sets and Systems. Theory and Application. Academic Press, New York, 1980.  
MR 0589341 
[5] Karpíšek Z., Pospíšek M., Slavíček K.: Properties of Certain Class of Fuzzy Numbers. Proc. $8^{th}$ Zittau Fuzzy Colloquium, Zittau (2000), 42–52, ISBN 3-00-006723-X. 
[6] Klir G. J., Yuan B.: 
Fuzzy Sets and Fuzzy Logic. Theory and Applications. Prentice Hall PTR, New Jersey, 1995.  
MR 1329731 | 
Zbl 0915.03001 
[7] Lukasová A.- Šarmanová J.: Methods of Clustering Analysis. SNTL Praha, 1985 (in Czech). 
[9] Novák V.: Fuzzy Sets and its Applications. SNTL Praha, 1986 (in Czech). 
[10] Späth H.: 
Cluster Dissection and Analysis. Ellis Horwood, 1985.  
Zbl 0584.62094 
[11] Zadeh L. A.: 
Fuzzy Sets and Their Application to Pattern Classification and Cluster Analysis. In Classification and Clustering, Academic Press, New York, 1977.  
MR 0483813 
[12] Žák L.: Fuzzy Clustering. Proc. Fuzzy logika - od metodiky k aplikacím, Hrubá Skála (1998), 81–87, (in Czech). 
[13] Žák L.: Clustering of Fuzzy Objects 1. Proc. Mendel 1999, $5^{th}$ International Conference on Soft Computing, Brno (1999), 310–317, ISBN 80-214-1131-7. 
[14] Žák L.: Clustering and Fuzzy Objects. Proc. Fuzzy logika - fuzzy logika, neuronové sítě a expertní systémy, Hrubá Skála (1999), 51–58, (in Czech). 
[15] Žák L.: Clustering of Fuzzy Objects 2.  Proc. Mendel 2000, $6^{th}$ International Conference on Soft Computing, Brno (2000), 310–317, ISBN 80-214-1131-7. 
[16] Žák L.: Fuzzy Objects and Fuzzy Clustering. Proc. $8^{th}$ Zittau Fuzzy Colloquium, Zittau (2000), 293–302, ISBN 3-00-006723-X. 
[17] Žák L.: Generalization Fuzzy Clustering for Fuzzy Objects. Proc. Inteligentní systémy pro praxi, Luhačovice (2000), 59–68, ISBN 80-238-6140-9 (in Czech). 
[18] Žák L.: 
Clustering of vaguely defined objects. PhD Thesis, Technical University, Brno, 2002, ISSN 1213-4198 (in Czech).   
MR 1982210 | 
Zbl 1122.62319