Herman Geuvers Rob Nederpelt Rewriting for Fitch Style Natural Deductions. 134-154 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3091&spage=134 2004 conf/rta/2004 RTA db/conf/rta/rta2004.html#GeuversN04