Xiaoshu Hang Honghua Dai Combining Extension Matrix and Integer Programming for Optimal Concept Learning. 352-360 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3157&spage=352 2004 conf/pricai/2004 PRICAI db/conf/pricai/pricai2004.html#HangD04