1. L.A Zadeh, ‘Fuzzy Sets’, Information and Control 8 (3) (1965), P. 338.
2. G. Frege, Grundgesetz der Arithmetik, Hildesheim: Georg Olms, 1962, p. 253.
3. W. V. Quine, ‘On Frege’s Way Out’, Mind, N. S. 64 (1955), 145–159.
4. S. Watanabe, ‘Logic of the Empirical World’, in C. Y. Cheng (ed.), Philosophical Aspects of the Mind-Body Problem, Honolulu: University of Hawaii Press, 1976, pp. 162–181. See in particular p. 169.
5. K. S. Fu, ‘Stochastic Automata as Models of Learning Systems’, in J. Tou (ed.), Computer and Information Science - II, New York: Academic Press, 1967, p. 177.