- K. Atanassov, Intuitionistic fuzzy sets, Fuzzy sets and systems 20 (1986) 87-96
- K. Atanassov, Modal and topological operators, defined over intuitionistic fuzzy sets, D. Shopov (ed.), Youth Scientific Contributions, Sofia, Vol 1 (1985) 18-21 (in Bulgarian)
- K. Atanassov, Intuitionistic fuzzy sets, V. Sgurev (ed.), VII ITKR's Session, Sofia, June 1983 (in Bulgarian)
- K. Atanassov and S. Stoeva, Intuitionistic fuzzy sets, Proc. of Polish Symposium on Interval and Fuzzy Mathematics, Poznan, Aug. 1983, 23-26
- A. Kaufmann, Introduction a la Theories des Sous-ensembles Flous (Masson, Paris-New York, 1977)
- H. Rasiowa and R. Sikorski, The Mathematics of Metamathematics, Polish Academy of Sciences, Warszawa, 1963.