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<article-title>Normative System Games</article-title>
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<author><a href="mailto:tag@hib.no"><name>Thomas &#197;gotnes</name></a></author>
<aff>Dept of Computer Engineering<br/> Bergen University College PB. 2030, N-5020 Bergen Norway</aff>

<author><a href="mailto:wiebe@csc.liv.ac.uk"><name>Wiebe van der Hoek</name></a></author>
<aff>Dept of Computer Science <br/>University of Liverpool Liverpool L69 7ZF UK</aff>

<author><a href="mailto:mjw@csc.liv.ac.uk"><name>Michael Wooldridge</name></a></author>
<aff>Dept of Computer Science <br/>University of Liverpool Liverpool L69 7ZF UK</aff>
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<title>ABSTRACT</title>
<p>We develop a model of normative systems in which agents are assumed
to have multiple goals of increasing priority, and investigate
the computational complexity and game theoretic properties of
this model. In the underlying model of normative systems, we use
Kripke structures to represent the possible transitions of a multiagent
system. A normative system is then simply a subset of the
Kripke structure, which contains the arcs that are forbidden by the
normative system. We specify an agent's goals as a hierarchy of
formulae of Computation Tree Logic (CTL), a widely used logic
for representing the properties of Kripke structures: the intuition is
that goals further up the hierarchy are preferred by the agent over
those that appear further down the hierarchy. Using this scheme,
we define a model of ordinal utility, which in turn allows us to
interpret our Kripke-based normative systems as games, in which
agents must determine whether to comply with the normative system
or not. We then characterise the computational complexity of
a number of decision problems associated with these Kripke-based
normative system games; for example, we show that the complexity
of checking whether there exists a normative system which has
the property of being a Nash implementation is NP-complete.</p>
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