[1] S. C. KLEENE: Introduction to Metamathematics. Van Nostrand, New York, 1952. MR 0051790 | Zbl 0047.00703

[2] P. HÁJEK K. BENDOVÁ Z. RENC: The GUHA method and the three-valued logic. Kybernetika 7 (1971),421-435. MR 0324940

[3] P. HÁJEK T. HAVRÁNEK: Mechanizing Hypothesis Formation. (Mathematical Foundations for a General Theory), Springer-Verlag 1978. MR 0501342

[4] J. P. CLEAVE: The notion of logical consequence in the Logic of inexact predicates. Zeitschr. Math. Logik Grundlagen Math. 20 (1974), 307-324. MR 0373828 | Zbl 0299.02015

[5] D. SCOTT: Combinators and Classes. Lambda-Calc. Comput. Sci. Theory, Proc. Symp., Rome 1975, Lecture Notes in Computer Science 37 (1975), 1-26. MR 0505296 | Zbl 0342.02018

[6] S. A. KRIPKE: A completeness theorem in modal logic. J. Symb. Logic 24 (1959), 1-14. MR 0110638 | Zbl 0091.00902

[7] R. PETS: Modal logics. Paris (1965).

[8] W. LIPSKI: On the logic of incomplete information. in: Mathematical Foundations of Computer Science 1977 (J. Gruska, Ed.), Lecture Notes in Computer Science 53, Springer-Verlag, Berlin 1977, 374-381. MR 0460106 | Zbl 0363.02025