1. On axiomatizability within a system;Craig;The Journal of Symbolic Logic,1953
2. Degrees of unsolvability associated with classes of formalized theory;Feferman;The Journal of Symbolic Logic,1957
3. Some applications of the notions of forcing and generic sets;Feferman;Fundamenta Mathematicae,1965
4. Semirecursive sets and positive reducibility;Jockusch;Transactions of the American Mathematical Society,1968
5. A note on degrees of partial functions;Myhill,1961