Dealing with concurrent actions in modal action logic

In this paper we present an approach for dealing with concurrent actions based on a modal action theory. It is an extension of the approach presented in a previous paper in which modalities are used to represent actions, and causal rules are introduced to address the ramification problem. An abductive semantics is adopted to deal with persistency. In this paper we extend the action language by introducing two different modalities for dealing with "open" and "closed" actions. Moreover, we show that causal rules play a crucial role for modelling concurrent actions.