Wolfram Kahl Basic Pattern Matching Calculi: a Fresh View on Matching Failure. 276-290 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2998&spage=276 2004 conf/flops/2004 FLOPS db/conf/flops/flops2004.html#Kahl04