# A Logic for Global and Local Announcements

arXiv: https://arxiv.org/abs/1707.08735 · HTML: https://mlsanity.com/paper/1707.08735/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 27 Jul 2017.

## Built on by (most cited first, 1 of 1)

- [De Re Updates](https://mlsanity.com/paper/2106.11497/) (2021)

## Abstract (arXiv)

In this paper we introduce em global and local announcement logic (GLAL), a dynamic epistemic logic with two distinct announcement operators -- [φ]^+A and [φ]^-A indexed to a subset A of the set Ag of all agents -- for global and local announcements respectively. The boundary case [φ]^+Ag corresponds to the public announcement of φ, as known from the literature. Unlike standard public announcements, which are em model transformers, the global and local announcements are em pointed model transformers. In particular, the update induced by the announcement may be different in different states of the model. Therefore, the resulting computations are trees of models, rather than the typical sequences. A consequence of our semantics is that modally bisimilar states may be distinguished in our logic. Then, we provide a stronger notion of bisimilarity and we show that it preserves modal equivalence in GLAL. Additionally, we show that GLAL is strictly more expressive than public announcement logic with common knowledge. We prove a wide range of validities for GLAL involving the interaction between dynamics and knowledge, and show that the satisfiability problem for GLAL is decidable. We illustrate the formal machinery by means of detailed epistemic scenarios.