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Unformatted text preview: S A for any w A . (30%) 2. Prove Proposition 1.11.9 in the notes: Let S be any set of ws and A,B any ws. Then: S { A } B i S { B } A. (40%) 3. (i) Show that ( A B ) A and ( A B ) B (ii) Prove Lemma 1.11.12 in the notes: If S is a formally consistent and complete set of formulas and is the valuation dened by ( p i ) = ( 1 , if p i S , if p i 6 S, then for any formula A , ( A ) = 1 i A S. 1...
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 Spring '09
 InessaEpstein
 Math, Logic

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