2.4 Extending the Classical Representation 39
language so that the only nonatomic formulas allowed must be true everywhere.
However, because we are restricting the language to finite domains, formulas such
as Formula 2.3 can be dealt with using an expansion of the formula into its corre-
sponding ground atoms. This technique is also applied to quantified formulas in
effects of operators (see Section 2.4.3).
Although some of the original approaches to AI planning were based on
axiomatic inference [249], many classical planners do not use it. This is mainly
in order to avoid complications such as the ones described above. As a general
rule, it is much easier to use axiomatic inference in planners that keep track of the
current state, which is something ...