Jeremy Pickens contributed to this post.
Jeremy did a great job of presenting our Reverted Indexing paper, but the short session made it difficult to answer all questions and comments thoroughly. For example, William Webber wrote up a post summarizing our work, in which he observed
The authors surmise that the reverted index is more effective because it suggests more selective expansion terms, and they reproduce example term sets as evidence. This explanation is convincing enough as far as it goes; but what is not explained is why the reverted index’s expansion terms are more selective. The reason is not obvious. A single-term reverted index is not much more than a weighted direct index, mapping from documents to the terms that occur in them
I would like to address his comments because this is a key aspect of Reverted Indexing.