Eight-stage process - conjunctive normal forms, Computer Engineering

Eight-stage process - Conjunctive normal forms:

Hence we notice the following eight-stage process converts any sentence with CNF as: 

1.  Eliminate all arrow connectives by rewriting into 

      P ↔ Q    =>   (P  →Q) ^  (Q → P)

      P → Q   =>   ¬P ? Q

2.  Just move ¬ inwards requiring De Morgan's laws in inc. quantifier versions and double

3.  Here rename variables apart: as the same variable name may be reused several times for different variables, contained by one sentence or between several. However to avoid confusion later rename each distinct variable into a unique name. 

4. Now move quantifiers outwards: as the sentence is now in a form whether all the quantifiers can be moved safely to the outside else affecting the semantics, which are provided they are kept in the same order. 

5. Skolemise existential variables  by replacing them into  Skolem constants and functions. But this is similar to the existential elimination rule from the last lecture: as we just substitute a term for each existential variable such are represents the 'something' for that it holds. Suppose if there are no preceeding universal quantifiers the 'something' is a fresh constant. Moreover, if there are then we use a function that takes all these preceeding universal variables as arguments then we're done we just drop all the universal quantifiers. Thus this types  leaves a quantifier-free sentence.

Posted Date: 1/11/2013 6:17:44 AM | Location : United States







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