14. The system of claim 13 , wherein the operations comprise selecting a subset of documents in the corpus, wherein the first value represents a quantity of documents in the subset that include a list that contains both terms of the pair, and wherein the second value represents a quantity of the documents in the subset that include a list that contains at least one of the terms of the pair.
14. The system of claim 13 , wherein the operations comprise selecting a subset of documents in the corpus, wherein the first value represents a quantity of documents in the subset that include a list that contains both terms of the pair, and wherein the second value represents a quantity of the documents in the subset that include a list that contains at least one of the terms of the pair. 15. The system of claim 14 , wherein selecting a subset of documents in the corpus comprises: determining an author for each document in the corpus; and selecting a subset of documents in the corpus that each have a different author.