1. Stig Kanger, Provability in Logic, Almquist & Wiksell, Stockholm, 1957; ‘A Note on Quantification and Modalities’ and ‘On the Characterization of Modalities’, both in Theoria
23 (1957).
2. Jaakko Hintikka, ‘Modality and Quantification’, Theoria
27 (1961), and The Modes of Modality’, Acta Philosophica Fennica
16 (1963).
3. Saul Kripke, ‘A Completeness Theorem in Modal Logic’, The Journal of Symbolic Logic
24 (1959), and ‘Semantical Analysis of Modal Logic I’, Zeitschrift für mathematische Logik und Grundlagen der Mathematik
9 (1963).
4. Richard Montague, ‘Logical Necessity, Physical Necessity, Ethics, and Quantifiers’, Inquiry
3 (1960).
5. J. Barkley Rosser, Logic for Mathematicians, McGraw-Hill, New York, 1953, Chapter IV, pp. 55–76.