Jean Berstel Luc Boasson Olivier Carton Bruno Petazzoni Jean-Eric Pin Operations Preserving Recognizable Languages. 343-354 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2751&spage=343 2003 conf/fct/2003 FCT db/conf/fct/fct2003.html#BerstelBCPP03