1. Lukasiewicz, J.: O Logice Trojwartosciowej. Ruch filoseficzny (Lwow) 5, 169–171 (1920)
2. Post, E.: Introduction to a general theory of elementary propositions. Am. J. Math. 43, 163–185 (1921)
3. 1. Chubaryan, A.: Relative efficiency of some proof systems for classical propositional logic. In: Proceedings of NASA RA, Vol. 37,N5, 2002, and Journal of CMA
4. 2. (AAS), Vol. 37, N5, pp. 71-84 (2002)
5. Mendelson, E.: Introduction to Mathematical Logic. Van Nostrand, Princeton (1975)