Axiom 
defines a total
order Better on the set of
appropriate mental actions for a
mental situation. The predicate
is true
if mental action 
is better
than mental action 
at mental
situation m. Therefore,
will be selected before at
mental situation m in the process
of searching for a solution.
The preference relation Better
is a powerful mechanism for the
declarative formalization of heuristics
[10] [2]
[17] [16]. Here
we use only two simple heuristics:
(1) actions appropriate for goals in upper
levels of the goal stack
are
preferred to actions appropriate for goals
in lower levels; (2) if two actions are
appropriate for the same goals, they are
selected in alphabetic order 
.
