cs245-asn2 - argument is invalid(a Natural Deduction c d a...

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CS 245 Winter 2009 Assignment 2 Due: Thu 29 Jan 2009 10am in the CS245 Drop Boxes 30 marks You must submit your assignment with a cover page produced using makeCover , otherwise you will lose 2 marks. Assignments are to be completed individually. The policy on academic ofenses is on the course web page. 1. (25 marks) For each o± the ±ollowing problems, determine whether the argument is valid or invalid. I± it is valid, prove its validity using the indicated proo± method (natural deduction or semantic tableaux). I± it is invalid, provide a counterexample and demonstrate that the
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Unformatted text preview: argument is invalid. (a) Natural Deduction: ( c d ) , a b c, b d | = ND a (b) Natural Deduction: ( c b ) a | = ND a b c (c) Natural Deduction: ( a b ) , b c | = ND a c (d) Semantic Tableaux: ( c d ) a, d a | = ST a c (e) Semantic Tableaux: ( a d ) , a b | = ST b d 2. (5 marks) Prove the ollowing set o ormulas is inconsistent using semantic tableaux: ( a b ) , a c, c 1...
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