1. Only works actually referred to are listed here.
2. Belnap, Nuel, and T. B. Steel, 1976, The Logic of Questions and Answers. Yale U. P., New Haven.
3. Beth, E. W., 1953, “On Padua’s Method in the Theory of Definition,” Indagationes Mathematicae vol. 15, pp. 330–339.
4. Beth, E. W., 1955, “Semantic Entailment and Formal Derivability,” Mededelingen van de Koninklijke Nederlandske Akademie van Wetenschappen, Afd. Letterkunde N. R. vol. 18, no. 13, pp. 309–342.
5. Bromberger, Sylvain, 1992, On What We Know When We Don’t Know: Explanation, Theory, Linguistics, and How Questions Shape Them, University of Chicago Press.