20. The method of claim 19 , wherein choosing the particular query comprises, if the partial cost does not satisfy the first particular mathematical relationship with the current-best cost or if the second cost satisfies a second particular mathematical relationship with the current-best cost, then choosing as the particular query a candidate query other than the certain query.
20. The method of claim 19 , wherein choosing the particular query comprises, if the partial cost does not satisfy the first particular mathematical relationship with the current-best cost or if the second cost satisfies a second particular mathematical relationship with the current-best cost, then choosing as the particular query a candidate query other than the certain query. 21. The method of claim 20 , wherein the second particular mathematical relationship is “greater than”.