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In-Depth Information
(
s
2
)
causes
if
:ab
2
up
broken
causes
ab
1
if
>
broken
From
ab
1
2 Res
([
toggle
(
s
2
)]) it follows that toggling
s
1
in that state fails
to produce the otherwise expected indirect eect
. Hence, the only
acceptable state which can be assigned to
Res
([
toggle
(
s
2
)
;
toggle
(
s
1
)]) is
f
up
(
s
1
)
;
up
(
s
2
)
; :
light
;
broken
; :
wiring-problem
; :
malfunc
1
; :
malfunc
2
; ab
1
; :ab
2
g
Consequently, (
O; D
) entails the observation
light
:
after [
(
s
2
)
;
(
s
1
)]
light
toggle
toggle
as expected.
4.4 Bibliographic Remarks
By the time this topic was written the problem of ramications having excep-
tions had received little attention in literature, presumably because satisfac-
tory solutions to the Ramication Problem itself had not emerged until very
recently. The proposal to combine solutions to both the Ramication and
Qualication Problem has been made in [112, 114]. About the only other pa-
pers on that topic are [5, 123]. In both of them expressions resembling causal
relationships are allowed to be defeasible. The former presents a formal action
theory, whose semantics is, however, indirectly dened via a translation into
extended logic programs and by appealing to the notion of answer sets [32].
The latter does not go beyond dening a notion of successor state based on
minimizing abnormality. In order to successfully cope with qualied rami-
cations, therefore, the general approach needs to be adopted of minimizing
abnormality in the initial state so that persistence and ramication take care
of the further evolution.
