1. B. R. Boričić, ‘A cut-free Gentzen-type system for the logic of the weak law of excluded middle’, to appear inStudia Logica.
2. W. Craig, ‘Linear reasoning. A new form of the Herbrand—Gentzen theorem’,Journal of Symbolic Logic 22 (1957), 250–268.
3. H. B. Curry,Foundations of Mathematical Logic, McGraw-Hill, New York, 1963.
4. T. Hosoi, ‘The separation theorem on the classical system’,Journal of the Faculty of Science, University of Tokyo 12 (1966), 223–230.
5. T. Hosoi, ‘Algebraic proof of the separation theorem on classical propositional calculus’,Proceedings of the Japan Academy 42 (1966), 67–69.