Subset Space Logic with Arbitrary Announcements
In this paper we introduce public announcements to Subset Space Logic (SSL). In order to do this we have to change the original semantics for SSL a little and consider a weaker version of SSL without the cross axiom. We present an axiomatization, prove completeness and show that this logic is PSPACE-complete. Finally, we add the arbitrary announcement modality which expresses ``true after any announcement'', prove several semantic results, and show completeness for a Hilbert-style axiomatization of this logic.