Jianfeng Feng The Minimum-Variance Theory Revisited. 62-69 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2686&spage=62 2003 conf/iwann/2003-1 IWANN (1) db/conf/iwann/iwann2003-1.html#Feng03