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showing logical argument is valid or invalid

  1. $p\to q$
    $q\to (r \lor \lnot p)$
    $\lnot r$
    therefore, $\lnot p$

  2. $p\to (r \lor q)$
    $q\to\lnot r$
    $r$
    therefore, $p$

I believe (1) is valid and (2) invalid. Am I correct?

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    You are correct, and the full truth tables will demonstrate that.2012-09-18

2 Answers 2