Strategic logics : complexity, completeness and expressivity

by transferring normative attributes from an agent to another. Such interactions are called delegation. Formal models of delegation and control were studied in, e.g., [189, 149, 191]. In this work, we consider the scenario where agents delegate control over propositions to other agents. The distinction between controllable and uncontrollable propositions stems from areas like discrete event systems and control theory, where, e.g., Boutilier [39] studied control in the context of deontic logic. Control and controllable propositions were also studied in [52, 66, 249, 248]. We now give an overview of the thesis. The main purpose of Chapter 2 is to introduce basic concepts and notation and to review relevant literature. The first section presents a brief survey on modal logic. Then, in sections 2.2, 2.3 and 2.4, we introduce epistemic, temporal and strategic modal logics and state known results that characterise their expressivity and computational complexity. In particular, we consider variants of ATL as extensions of branching-time logics. With such ATL-like logics we can describe dynamic multi-agent interactions. In Section 2.5, we discuss extensions of ATL with epistemic notions. Additionally, we suggest a framework for memory-bounded strategic reasoning. In particular, we introduce an epistemic variant of ATL that accounts for agents with limited memory resources as this case was neglected in the literature to date. In Chapter 3, we investigate the computational complexity of ATL and its epistemic extension ATEL. We show in detail how 'the complexity of the satisfiability problem for both logics can be settled at ExpTIME-complete. The part of the chapter about ATL is based on the paper 'ATL Satisfiability is Indeed ExpTIME-COmplete' by Walther, Lutz, Wolter and Wooldridge in the Journal of Logic and Computation, 2006 (265)' and the part about ATEL is based on the paper 'ATEL with Common and Distributed Knowledge is ExpTime-Complete' by Walther which was presented at the 4th Workshop on Methods for Modalities, Humbolt University, Berlin, December 1-2, 2005 [264]. In Chapter 4, we aim to extend the expressiveness of ATL without increasing its computational complexity. We introduce explicit names for strategies in the object language and extend modal operators with the possibility to bind agents to strategy names. In this way, we can fix the decisions of agents that possibly belong to several coalitions. By identifying the behaviqur of agents, we can reason about the effects of agents changing coalitions. Dynamic coalitions provide more flexibility to adapt abilities to a changing environment. We investigate the expressivity of the resulting logic ATLES and compare it to ATL and ATL*. Moreover, we formulate two model checking problems for ATLES and investigate their complexity as well as the complexity of the satisfiability problem for ATLES. Additionally, we present a complete axiomatisation. This chapter is based on the paper 'Alternating-time Temporal Logic with Explicit Strategies' by Walther, van der Hoek and Wooldridge which is going to presented at the 11th Conference on Theoretical Aspects of Rationality and Knowledge (TARK), Brussels, Belgium, June 25-27, 2007 [266]

Discovering a Better Way: The Need for Effective Civil Litigation Reform

This Article addresses the myriad problems posed by unfettered discovery in the United States Rather than promoting fairness and efficiency in the American legal system, plaintiffs today often use discovery in an abusive and vexatious manner to coerce defendants into accepting quick settlements Over the past several decades, discovery has expanded in both scope and magnitude such that discovery costs now account for at least half of the total litigation costs in any given case The advent of electronic discovery has only exacerbated the problem, given the sheer number of electronic documents generated in the course of business and the corresponding time, effort, and cost associated with electronic discovery Although recent efforts to amend the Federal Rules of Civil Procedure have failed to combat the abuses of civil discovery, meaningful and effective reform of the current system is possible This Article proposes a number of pragmatic reforms-including adopting the English rule for discovery disputes and suspending discovery during the pendency of a motion to dismiss-to mitigate the abusive and costly nature of discovery in the United State

Crisis-Driven Tax Law: The Case of Section 382

At the peak of the 2008 financial crisis, the Internal Revenue Service (IRS) issued Notice 2008–83 (the Notice), administrative guidance that limited Internal Revenue Code (the Code) section 382, an important tax rule designed to discourage tax-motivated acquisitions. Although styled as a mere interpretation of existing law, the Notice has been widely viewed as an improper exercise of the IRS’s authority that undermined its legitimacy. But did the Notice work? There were many extraordinary interventions during the financial crisis that raised questions about eroding the rule of law and the long-term destabilizing effects of bailouts. In a financial crisis, regulators must weigh these real, but distant and uncertain, costs against the immediate benefits of the intervention. Toward that end, we report the first evidence of the effects of limiting Code section 382 during the 2008 financial crisis. Although we find little evidence that the Notice affected bank merger activity, those mergers that occurred while the Notice was in effect produced lower post-merger income growth. The results suggest that Code section 382 may have some benefits in terms of discouraging tax-motivated acquisitions. We use the Notice to illustrate the concerns that should guide lawmakers’ decisions about if and how to make law during a crisis