Richard Montague. Syntactical treatments of modality, with corollaries on reflexion principles and finite axiomatizability. Proceedings of a Colloquium on Modal and Many-valued Logics, Helsinki, 23-26 August, 1962, Acta philosophica Fennica, no. 16, Helsinki 1963, pp. 153–167.

Richard Montague. Syntactical treatments of modality, with corollaries on reflexion principles and finite axiomatizability. Proceedings of a Colloquium on Modal and Many-valued Logics, Helsinki, 23-26 August, 1962, Acta philosophica Fennica, no. 16, Helsinki 1963, pp. 153–167. - Volume 40 Issue 4