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Logic and the set theory - Lecture 9: Predicate Calculus

Logic and the set theory - Lecture 9: Predicate Calculus

Logic and the set theory - Lecture 9: Predicate Calculus

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Inference rules for <strong>the</strong> universal quantifiersExamplesFa A. ⊢ ∀xAx. This is incorrect.∀x(Fx → Gx), Fa → Ga, : Fa : Ga, : ∀xGx, Fa → ∀xGx. This isincorrect.∀xLxx A., Laa, ∀zLza. This is incorrect.∀x(Fx ∧ Gx) ⊢ ∀xFx ∧ ∀xGx.Proof: 1. ∀x(Gx ∧ Fx) A.2. Fa ∧ Ga from 1.3. Fa.4. Gb.5. ∀xFx.6. ∀xGx.S. Choi (KAIST) <strong>Logic</strong> <strong>and</strong> <strong>set</strong> <strong>the</strong>ory October 7, 2012 8 / 26

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