1. On Padoa's method in the theory of definition;Beth;Indagationes Mathematicae,1953
2. Einige methodologische Untersuchungen iiber die Definierbarkeitder Begriffe;Tarski;Erkenntnis,1935
3. Grundlagen der Mathematik;Hilbert,1939
4. On the Metamathematics of Algebra, Studies in Logic and theFoundations of Mathematics;Robinson,1951