[1] Church Alonzo: Introduction to Mathematical Logic, Part. I. Princeton University Press, Princeton 1956. MR 1435972

[2] Gentzen Gerhardt: Untersuchungen über das logische Schliessen. Mathem. Zeitschrift 39 (1934-35), 176-210, 405-431.

[3] Hao Wang: A Survey of Symbolic Logic. Science Press, Peking; North Holland Publishing Co., Amsterdam 1962.

[4] Kramosil Ivan: A Method for Random Sampling of Well-Formed Formulas. Kybernetika 8 (1972), 2, 135-148. MR 0343414 | Zbl 0242.02014

[5] Kramosil Ivan: Statistical Estimation of Deducibility in Polyadic Algebras. Kybernetika 7 (1971), 3, 181-200. MR 0300881

[6] Davis Martin: Conputability and unsolvability. McGraw Hill Book Company, New York, Toronto, London 1958. MR 0124208

[7] Kleene Stephen Cole: Introduction to Metamathematics. D. van Nostrand Company, New York, Toronto 1952. MR 0051790

[8] van Westrhenen S. C.: A probabilistic machine for the estimation of Probability in the first order predicate calculus. Zeitschr. für Math. Logik and Grundlagen der Math. 15 (1969), 291-297. MR 0263635

[9] van Westrhenen S. C.: Statistical Studies of Theoremhood in Classical Propositional and First-Order Predicate Calculus. Journal of the Association for Computing Machinery 19 (1972), 2, 347-365. MR 0297524 | Zbl 0246.68017