Abstract: An information retrieval system including a user operated computer having a display and a storage facility, a search back-end containing an index into a collection of documents, the index defining results sets of queries relative to the collection of documents, and a search application stored in the storage facility which is executable by the computer to perform a method of providing a cooperative answer to a query submitted by the user, the submitted query having an empty result set, the cooperative answer comprising subqueries of the submitted query and, for each subquery, cardinality information indicative of whether the subquery has an empty result set.