1. Aquinas, Thomas,Summa Theologiae, Latin text and English translation, Blackfriars, London, 1967.
2. G. Boolos,The Unprovability of Consistency, Cambridge, 1979.
3. G. Frege,Grundgesetze der Arithmetik, Bd. II, Wiss. Buchgesellschaft, Darmstadt, 1962 (Reprint form 1903).
4. M. B. Hesse, ?Theories and the Transitivity of Confirmation?, in:Philosophy of Science 37 (1970), p. 50?63.
5. J. Hintikka,Knowledge and Belief, Cornell University Press, New York, 1962.