The pool of relevant documents sits below the titles list to serve as a reminder of the books or abstracts which have been selected. Initially it was thought that users should be able to remove items from this list, but that proved very difficult to reconcile with the principle of incremental query expansion. If removal from the pool represents a change in an earlier relevance judgement, a corresponding change should be applied to the working query: namely the removal and / or re-weighting of those terms originally extracted from the document. So deletions from the pool are not permitted in the final system. Full details of documents in the pool are printed (or e-mailed) when the user clicks the Print or Mail button on the button bar.