1. A method comprising: searching a search space of a corpus to yield a plurality of results, the corpus comprising a plurality of documents associated with a plurality of keywords, each document associated with at least one keyword indicating at least one theme of the document; determining that one or more of the plurality of keywords are irrelevant keywords; expanding the irrelevant keywords to include one or more other keywords related to the irrelevant keywords by: determining one or more irrelevant themes indicated by the irrelevant keywords; identifying one or more affine themes that are highly affine to the irrelevant themes, wherein the affine themes are highly affine if they satisfy an affinity threshold; determining one or more affine keywords that correspond to the affine themes; and identifying the affine keywords as the keywords related to the irrelevant keywords; and refining the search according to the irrelevant keywords.