2250 Lecture Notes - If And Only If
5 Feb 2013
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Document Summary
The tree method of the logic book was designed to ensure that truth flows down along at least one branch of a tree. Supposing that all the members in a set of sentences are true, the decomposition rules only allow you to write down component or negated component sentences that are true on at least one branch. But the devil always lies and is very concerned that no truths be derived from his lies. Your job is to design an alternative tree method for the devil to use. As part of this, you should state the truth value assignments that would be made to negated and unnegated literals on an open tree branch, and the conditions under which a tree branch would close. Compare your results with those in the answer book for these same questions. What does this tell you: the devil does not like our concepts of truth functional equivalence, consistency, entailment, and validity.
