Alex Ferguson Derek G. Bridge Partial Orders and Indifference Relations: Being Purposefully Vague in Case-Based Retrieval. 74-85 http://link.springer.de/link/service/series/0558/bibs/1898/18980074.htm 2000 conf/ewcbr/2000 EWCBR db/conf/ewcbr/ewcbr2000.html#FergusonB00