As explained before, we use the
concept of a mental situation
in order to describe the internal
state of a system as it reasons
about a problem. A mental situation
of STRIPS m is characterized by
two atomic formulas:
(1) GS(i,g,m) is true if
subgoal g is at location i in the
goal stack associated with m;
(2) Current(m)=s is true if s is
the current situation described by the
database associated with m.
Notice that, we do
not need an explicit representation of
the database associated with a mental
situation, because axioms 
to allow us to compute
such a database from the description
of the current situation associated
with that mental situation.
Axioms and
describe how the initial mental
situation 
is constructed from
the representation of a planning problem.
The database associated with the initial
mental situation describes 
-the
problem's initial situation. The goal stack
contains a subgoal
of
the form 
for each formula
f that is in the stack describing
-the problem's goal situation-
and is not in the database associated
with the current situation (i.e., 
). The location numbers
of the subgoals in the goal stack are
the same as the location numbers of the
formulas they refer to in the stack
describing the problem's goal situation.
