In this paper wesuggest a wayof using the rules of System P to propagate lower bounds on conditional probabilities. Usinga knowledgebase of default rules whichart, consideredto be constraints on a probability distribut ion, the result of applyingthe rules of P gives us newconstraints that wereimplicit in the knowledge base and their associated lower bounds. 							
						
							
					 															
					Rachel A. Bourne, Simon Parsons