Elements of Intuitionism, 2000. ,
Semantical Investigations in Heyting's Intuitionistic Logic, chapter Consequence Relations, 1981. ,
The Collected Works of Gerhard Gentzen, chapter Investigations into Logical Deduction, 1969. ,
Introduction to Metamathematics, 1952. ,
Handbook of Logic in Artificial Intelligence and Logic Programming, chapter General Patterns in Nonmonotonic Reasoning, 1994. ,
Completeness and Axiomatizability in Many-Valued Logic, Proceedings of the Tarski Symposium, pp.411-435, 1974. ,
, chapter On Some Fundamental Concepts of Metamathematics, 1956.