Yasuhito Mukouchi Masako Sato Learning Languages Generated by Elementary Formal Systems and Its Application to SH Languages. 380-394 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3244&spage=380 2004 conf/alt/2004 ALT db/conf/alt/alt2004.html#MukouchiS04