Bryan Krawetz John Lawrence Jeffrey Shallit State Complexity and the Monoid of Transformations of a Finite Set. 213-224 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3317&spage=213 2004 conf/wia/2004 CIAA db/conf/wia/ciaa2004.html#KrawetzLS04