A Computationally Grounded Dynamic Logic of Agency, with an Application to Legal Actions

In this article, we propose a Dynamic Logic of Propositional Control DL-PC in which the concept of 'seeing to it that' (abbreviated stit) as studied by Belnap, Horty and others can be expressed; more precisely, we capture the concept of the so-called Chellas stit theory and the deliberatibe stit theory, as opposed to Belnap's original achievement stit. In this logic, the sentence 'group G sees to it that φ' is defined in terms of dynamic operators: it is paraphrased as 'group G is going to execute an action now such that whatever actions the agents outside G can execute at the same time, φ is true afterwards'. We also prove that the satisfiability problem is decidable. In the second part of the article we extend DL-PC with operators modeling normative concepts, resulting in a logic DL-PCLeg. In particular, we define the concepts of 'legally seeing to it that' and 'illegally seeing to it that'. We prove that the decidability result for DL-PC transfers to DL-PCLeg.