Ulisses Ferreira On the Foundations of Computing Science. 46-65 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3002&spage=46 2003 conf/metainformatics/2003 Metainformatics db/conf/metainformatics/metainformatics2003.html#Ferreira03