14. The storage medium of claim 12 , further comprising instructions for instantiating at least a third iterator to perform the at least one fact-level operation on at least the first and second candidate facts, wherein the third iterator is for communicating with the first and second iterators.
14. The storage medium of claim 12 , further comprising instructions for instantiating at least a third iterator to perform the at least one fact-level operation on at least the first and second candidate facts, wherein the third iterator is for communicating with the first and second iterators. 16. The storage medium of claim 14 , wherein the instructions for instantiating at least a third iterator include instructions for instantiating an iterator for performing a union or intersection operation on the first and second candidate facts.