Laurence Cholvy Christophe Garion An Attempt to Adapt a Logic of Conditional Preferences for Reasoning with Contrary-To-Duties. 183-204 2001 48 Fundam. Inform. 2-3 db/journals/fuin/fuin48.html#CholvyG01 http://iospress.metapress.com/content/rwc6p4wb4qyf6xrq/