[1] G. Lakoff, Hedges: A study in meaning criteria and the logic of fuzzy concepts. J. Philos. Logic 2 (1973), 458-508. MR 0421984

[2] J. K. Mattila: On modifier logic. In: Fuzzy Logic for the Management of Uncertainty (L.A. Zadeh and J. Kacprzyk, eds,), J. Wiley and Sons, New York, 1092, pp. 191-209.

[3] H. Rasiowa, R. Sikorski: The Mathematics of Metamat hematics. PWN, Warszawa 1963.

[4] P. C. Rhodes, S. M. Menani: Towards a fuzzy logic programming system: a fuzzy propositional logic. Knowledge-Based Systems 4 (1991), 1, 52-62.

[5] L. A. Zadeh: Fuzzy sets. Inform, and Control 8 (1965), 338 353. MR 0219427 | Zbl 0139.24606

[6] L. A. Zadeh: Fuzzy logic and approximate reasoning. Synthesis 30 (1975), 107-128. Zbl 0319.02016