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Unformatted text preview: EECS 203, Winter 2007 Discrete Mathematics Lecture 4 Rules of Inference and G¨ odel’s Theorems January 16 Reading: Rosen [1.5] January 16 Rules of Inference and G¨odel’s Theorems, Page 1 4.1 Review A model (or interpretation ) M for a first order logic L is a universe U together with an assignment of actual objects in U for each constant, variable, function, and predicate in L . We say that M satisfies φ , denoted by M φ , if φ M = True . A wff φ is said to be valid if it is satisfied by all models. Two wffs φ and ψ are logically equivalent if φ ←→ ψ is valid. The following wffs are valid. • A wff obtained from a propositional tautology by replacing each propositional variable by a wff. • ( ∀ xφ )→ φ [ x ← t ], for all wff φ and variable x , where φ [ x ← t ] is φ with all free x replaced by a term t . • φ→ ∀ xφ , for all wff φ with no free x . • ( ∀ x ( φ→ ψ ))→ (( ∀ xφ )→ ( ∀ xψ )), for all wffs φ , ψ and variable x . January 16 Rules of Inference and G¨odel’s Theorems, Page 2 4.1 Review • ¬∀ xφ ≡ ∃ x ¬ φ , • ¬∃ xφ ≡ ∀ x ¬ φ ....
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 Winter '07
 YaoyunShi

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