Fuzzy logic with unless-rules

Unless-rules are intended to deal with problems of reasoning with incomplete information and/or resource constraints. An unless-rule is proposed to be of the form `if X is A then Y is B unless Z is C´. Such rules are employed in situations in which the conditional statement if X is A then Y is B usually holds and the assertion Z is C holds rarely. Thus, using a rule of this type the exception condition can be ignored when the resources needed to establish its presence are tight or there simply is no information available as to whether it holds or does not hold. In this case of incomplete information, since it is the case that if X is A then Y is B usually holds, one may be willing to jump to the conclusion Y is B given that X is A because no information as to whether Z is C holds is available