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after [
(
s
1
)]
light
toggle
then
FC
(
O;D
)
includes the axiom
9s
[
Result
([
toggle
(
s
1
)]
;s
)
^ Holds
(
light
;s
)]
Let
t
s
be a term satisfying this conjunction, then axiom (2.37) implies
s
1
)
;t
s
)]
In turn, this and the fact that
Holds
(
light
;t
s
) imply
8s
[
Result
([ ]
;s
)
Successor
(
s;
(
toggle
8s
[
Result
([ ]
;s
)
s
=
:
up
(
s
1
)
up
(
s
2
)
:
light
]
according to axiom (2.40) and
FC
(
O;D
)
. Following axioms (2.35) and (2.38),
we thus conclude that
9s
[
Result
([ ]
;s
)
^:Holds
(
up
(
s
1
)
;s
)
^ Holds
(
up
(
s
2
)
;s
)
^:Holds
(
light
;s
)]
In other words, (
O; D
) entails the observation
:
up
(
s
1
)
^
up
(
s
2
)
^:
light
after []
2.10 Bibliographic Remarks
The Ramication Problem was introduced and so named in [37].
21
This ar-
ticle also contains the rst proposal for a solution, which in essence is a
specic realization of globally minimizing change. The authors themselves
already argued that this approach may suggest unrealistic indirect eects,
but no solution was oered. In [121] the idea was (informally) raised of in-
troducing some notion of preference as regards changes of specic fluents
over changes of other fluents. The rst formal realization of this approach
employed the concept of categorization [65]. The introduction of categories
as means to avoid unmotivated indirect eects has later on been used in a
variety of frameworks, accompanied by an inventiveness as regards names
for these categories|e.g.,
frame
vs.
non-frame
fluents [65, 57]; (the latter of
which introduces
AR
as an extension of the Action Description Language
A
mentioned in Section 1.3);
relevant
vs.
dependent
[14];
persistent
vs.
non-
persistent
[18];
remanent
vs.
dependent
[91];
inertial
vs.
non-inertial
[41]; or
persistent
,
remanent
and
contingent
fluents [17]. While all being based on the
principle of categorization, these approaches dier in the degree of sophisti-
cation. The most elementary use of categories is to distinguish two classes of
21
First published as [36]. The naming was inspired by [28], which was devoted to
the problem of how to exploit logical consequences (so-called \ramications"
(
sic
)) of goal specications in planning problems, with the aim of restricting
search space.
