The original paper contained an error in the definition of "optimal
rplan dependency graph" (Definition 1). A dependency (x,x') between
two variables was not recorded in case the responsible precondition on
x was already true in the state in question. That, however, is correct
only if x is not part of the graph and thus will not change its value.

The present paper corrects this error, as well as an implication it
had for the definition of "local dependency graph" (Definition 3). The
only proof that needed to be adapted was that of Lemma 3. All
experiments were re-run, and yielded exactly the same results as
before. The text was adapted in some places to reflect the changed
definitions.

Here is a brief change log:

-- Section 4: Minor changes to text of bullets (A) and (B); minor
   changes in rightmost column of Table 1.

-- Section 5: Corrected Definition 1 (adding two times "or x \in V
   \setminus \{x_0\}" in the middle paragraph). Extended the
   explanation directly below the definition. Introduced the notion of
   "inverse" transition in the context of "invertible transition"
   (unrelated to the error, helps to make text clearer).

-- Section 6: Corrected Definition 3 (adding "or x \in V \setminus
   \{x_0\}" one time in the middle paragraph).

-- Appendix A.2: Repeated definition of inverse/invertible for
   improved self-containedness. Corrected proof of Lemma 3 by
   extending the arguments in the induction proving properties (a) and
   (b).