1. Fitch {1952}. Symbolic Logic by F. B. Fitch (the Ronald Press Company New York). Fitch {1952}. Symbolic Logic by F. B. Fitch (the Ronald Press Company New York).
2. Shoenfield {1967}. Mathematical Logic by Joseph R. Shoenfield (Addison-Wesley). Shoenfield {1967}. Mathematical Logic by Joseph R. Shoenfield (Addison-Wesley).