1. Theorie der Logischen Auswahlfunktionen
2. Hilbert's ?-operator and classical logic
3. Hilbert's ε-operator in intuitionistic type theories
4. and , A Course in Mathematical Logic. North-Holland Publ. Comp., Amsterdam 1977.
5. , and , Logic, Bivalence and Denotation, Ridgeview Publishing, Astacadero, Calif., 1986.