Modal correspondence theory in the class of all Euclidean frames
Philippe Balbiani, Dimiter Georgiev, Tinko Tinchev · Journal of Logic and Computation · 2017
The core of this article is the modal correspondence theory in the class of all Euclidean frames. It shows that with respect to the class of all Euclidean frames, every modal formula is first-order definable and the problem of deciding the modal definability of sentences is undecidable.