1. Fuzzy Sets and Systems;Dubois,1980
2. Algebraic Theory of Automata;Ginzburg,1968
3. Algebraic Automata Theory;Holcombe,1982
4. N. Honda, M. Nasu, S. Hirose, F-recognition of fuzzy languages, in: M.M. Gupta et al. (Eds.), Fuzzy Automata and Decision Processes, 1977, pp. 149–168.