Dear all,

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

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Speaker: Dr. Ringo Baumann

Universität
Leipzig

https://www.informatik.uni-leipzig.de/~baumann/

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# 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)

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

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ABSTRACT:

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).

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

--
TU Wien
Institut für Logic & Computation
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