Daniel Reidenbach On the Learnability of E-pattern Languages over Small Alphabets. 140-154 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3120&spage=140 2004 conf/colt/2004 COLT db/conf/colt/colt2004.html#Reidenbach04