Want to take part in these discussions? Sign in if you have an account, or apply for one below
Vanilla 1.1.10 is a product of Lussumo. More Information: Documentation, Community Support.
Thanks.
I have added a link to this from modal logic.
I’m not really understanding the theorem, but it sounds similar to the Birkhoff characterization of equational varieties.
I am away from base so cannot check, but I seem to remember that it is exactly a relational version of Birkhoff’s theorem. There is a survey of Algebraic Polymodal Logic by Goldblatt that I have used and I remember that it has a discussion of the theorem. Note there is a paper linking the theorem with coalgebras. It starts:
”The Goldblatt-Thomason theorem [11] states that a class of Kripke frames closed under ultrafilter extensions is modally definable if and only if it reflects ultrafilter extensions and is closed under generated subframes, homomorphic images and disjoint unions….”
1 to 4 of 4