dlm@allegra.att.COM (11/16/88)
Dr. Wiktor Marek
Department of Computer Science
University of KY
Monday, 11/21, 1:30 PM
AT&T Bell Laboratoris - Murray Hill 3D-473
On the Semantics of Default Logic
At least two different types of structures have been
proposed as correct semantics for logic of defaults:
Minimal sets of formulas closed under defaults and fixed
points of Reiter's operator GAMMA. In some cases these
notions coincide, but generally this is not the case. In
addition Konolige identified Reiter's fixed points (so
called extensions) with a certain class of autoepistemic
expansions of Moore.
We identify another class of structures for defaults,
called weak expansions and show a one to one correspondence
between Moore's autoepistemic expansions and weak expan-
sions. This functor extends Konolige's correspondence. We
show that the expressive power of autoepistemic logic (with
expansions as the intended structures) is precisely same as
default logic with weak expansions.
Sponsor: D. Etherington - ether@allegra.att.com