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Unformatted text preview: (F • H) need f or h to be false 1 st try to prove invalidity E, F, G, H F, F, T, T Invalid Indirect proofs assume negation, derive contradiction B [(O v ~O) (T v U)] U ~(G v ~G) ~(B T) IP ~(~B v T) Imp, 3 ~~B • ~T 4, DeM ~~B 5, Simp B 6, DN (O v ~O) (T v U) 1, 7 MP B v ~O 7, Add ~O v B 8, Comm O B imp, 10 O (O•B) 11, Abs ~O v (O•B) 12, Impl lj(~O v O) • (~O v B) Dist, 13 ~O v O 14, Simp O v ~O comm, 15 T v U MP 16, 8 ~T • ~~B comm, 5 ~T Simp, 18 U 17, 19 DS ~(G v ~G) MP 2, 20 ~G • ~~G...
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 Fall '07
 Hopper
 Logic, Invalid Indirect proofs

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