Belief Shadowing Łukasz Białek 1 , Barbara Dunin-Kęplicz 1 , and Andrzej Szałas 1,2(B ) 1 Institute of Informatics, University of Warsaw, Warsaw, Poland {bialek,keplicz,andrzej.szalas}@mimuw.edu.pl 2 Department of Computer and Information Science, Linköping University, Linköping, Sweden Abstract. Adapting beliefs to new circumstances, like belief change, update, revision or merging, typically requires deep and/or complex adjustments of belief bases even when adaptations happen to be tran- sient. We present a novel, lightweight and tractable approach to a new kind of beliefs’ interference which we call belief shadowing. Put simply, it is a transient swap of beliefs when part of one belief base is to be shad- owed by another belief base representing new observations and/or beliefs of superior agents/teams. In this case no changes to belief bases are needed. This substantially improves the performance of systems based on doxastic reasoning. We ensure tractability of our formal framework, what makes it suitable for real-world applications. The presented approach is based on a carefully chosen four-valued paraconsistent logic with truth values representing truth, falsity, incom- pleteness and inconsistency. Moreover, potentially undesired or forbid- den conclusions are prevented by integrity constrains together with their shadowing machinery. As an implementation environment we use 4QL Bel , a recently devel- oped four-valued query language based on the same underlying logic and providing necessary reasoning tools. Importantly, the shadowing tech- niques are general enough to be embedded in any reasoning environment addressing related phenomena. 1 A New Perspective on Belief Change When agents act in dynamic environments, belief change/revision/update/ merging is inevitable, creating a multitude of problems of theoretical and applied nature [7, 27, 35]. In the case of group beliefs, like in teamwork, the situation becomes even more complex [13]. In real-world applications, beliefs are contextual, and affected socially, psychologically and emotionally. Some, like “do not harm”, are hardly mutable but others, like “avoid slippery surfaces”, meant as an indication, are flexible. In fact, known theories of belief update/change/revision/merging do not distinguish between the rigid and transient beliefs. However, in everyday activ- ities we temporarily adjust our beliefs to specific situations with no intention to Supported by the Polish National Science Centre grant 2015/19/B/ST6/02589, the ELLIIT network organization for Information and Communication Technology, and the Swedish Foundation for Strategic Research (SymbiKBot Project). c  Springer Nature Switzerland AG 2019 D. Weyns et al. (Eds.): EMAS 2018 Workshops, LNAI 11375, pp. 158–180, 2019. https://doi.org/10.1007/978-3-030-25693-7_9