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Reminder - Talk announcement: Thursday, Nov 28, 2019, 12:00 c.t.: Ringo Baumann "An Abstract, Logical Approach to Characterizing ..."

Dear all,

the Institute of Logic and Computation cordially invites you to the following talk:


Speaker: Dr. Ringo Baumann

Universität Leipzig


                               DATE:   Thursday, November 28, 2019

                                        TIME:   12:00 s.t.

 VENUE: Seminarraum FAV EG C (Seminarraum Gödel), Favoritenstraße 9-11, 1040 Wien, RoomNo.: HB EG
                               10 (ground floor, access from yard)


    TITLE: An Abstract, Logical Approach to Characterizing Strong Equivalence in Non-monotonic
                               Knowledge Representation Formalisms


Two knowledge bases are strongly equivalent if and only if they are mutually interchangeable in
arbitrary contexts. This notion is of high interest for any logical formalism since it allows one
to locally replace, and thus give rise for simplification, parts of a given theory without
changing the semantics of the latter. In contrast to classical logic where strong equivalence
coincides with standard equivalence (having the same models), it is possible to find ordinary but
not strongly equivalent objects for any nonmonotonic formalism available in the literature.
Consequently, much effort has been devoted to characterizing strong equivalence for knowledge
representation formalisms such as logic programs, Reiter's default logic, or Dung's argumentation
frameworks. For example, strong equivalence for logic programs under stable models can be
characterized by so-called HT-models. More precisely, two logic programs are strongly equivalent
if and only if they are standard equivalent in the logic here-and-there.

This means, the logic of here-and-there can be seen as a characterizing formalism for logic
programs under stable model semantics. The aim of this article is to study whether the existence
of such characterization logics can be guaranteed for any logic. One main result is that every
knowledge representation formalism that allows for a notion of strong equivalence on its finite
knowledge bases also possesses a canonical characterizing formalism. In particular, we argue that
those characterizing formalisms can be seen as classical, monotonic logics.

Moreover, we will not only show the existence of characterizing formalism, but even that the model
theory of any characterizing logic is uniquely determined (up to isomorphism).

With kind support of the Vienna Center for Logic and Algorithms (VCLA) and the Wolfgang Pauli
Institut (WPI).