Liara Aparecida dos Santos Leal Dalcidio Moraes Claudio Laira Vieira Toscani Paulo Blauth Menezes A Categorical Approach to NP-Hard Optimization Problems. 62-73 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2809&spage=62 2003 conf/eurocast/2003 EUROCAST db/conf/eurocast/eurocast2003.html#LealCTM03