[1] Hájek P.: Metamathematics of fuzzy logic. Kluwer, Dordrecht 1998. MR 1900263

[2] Klawonn F.: Fuzzy Points, Fuzzy Relations and Fuzzy Functions. In: Novák, V. and I. Perfilieva (eds): Discovering the World with Fuzzy Logic. Springer, Heidelberg 2000, 431-453. MR 1858110 | Zbl 1010.03045

[3] Klawonn F., R. Kruse: Equality Relations as a Basis for Fuzzy Control. Fuzzy Sets and Systems 54 (1993), 147-156. MR 1215115 | Zbl 0785.93059

[4] Novák V.: On functions in fuzzy logic with evaluated syntax. Neural Network World, 10 (2000), 869-875.

[5] Novák V.: On fuzzy equality and approximation in fuzzy logic. Submitted to Soft Computing.

[6] Novák V., Perfilieva I., J. Močkoř: Mathematical Principles of Fuzzy Logic. Kluwer, Boston 1999. MR 1733839

[7] Perfilieva I.: Normal Forms for Fuzzy Logic Relations and the Best Approximation Property. Proc. Joint. Conf. EUSFLAT-ESTYLF'99, Palma de Mallorca 1999, 39-42.

[8] Perfilieva I.: Normal Forms for Fuzzy Logic Functions and Their Approximation Ability. Fuzzy Sets and Systems 124 (2001), 371-384. MR 1860857 | Zbl 0994.03019

[9] Perfilieva I.: Fuzzy Relations, Functions, and Their Representation by Formulas. Neural Network World, 10 (2000), 877-890.

[10] Shoenfield J. R.: Mathematical Logic. New York: Addison-Wesley 1967. MR 0225631 | Zbl 0155.01102