1. W. Ackermann. Solvable Cases of the Decision Problem. 114 pp., 1954, Amslerdam.
2. Alonzo Church. Special cases of the decision problem, Revue philosophique de Louvain 49 (1951), 203–221
3. a correction, ibid., 50(1952), 270–272.
4. Alonzo Church. Introduction to Mathematical Logic, I. 376 pp., 1956, Princeton.
5. M. Davis and H Putnam. A computational proof procedure. AFOSR, 1959 (submitted to Journal of Association for Computing Machinery).