1. P. Bernays, Beiträge zur axiomatischen Behandlung des Logik-Kalküls; Habilitationsschrift. Presented to the Georg-August-Universität zu Göttingen on 9 July 1918 [Reprinted [24], pp. 222–268]
2. P. Bernays, Logical Calculus. Lecture Notes at the Institute for Advanced Study (1935/1936) [Notes by P. Bernays, with the assistance of F.A. Ficken; Princeton 1936. The notes can be found in the Bernays Nachlass of the ETH Zürich, HS973:6]
3. P. Bernays, Axiomatische Untersuchung des Aussagen-Kalküls der Principia Mathematica. Math. Z. 25, 305–320
4. W.W. Boone, An analysis of Turing’s ‘The word problem in semi-groups with cancellation’. Ann. Math. 67, 195–202 [Reprinted [76], pp. 175–182]
5. A. Church, An unsolvable problem of elementary number theory (abstract). Bull. Am. Math Soc. 41, 333