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Homework Help: Proof of De Morgan's law

  1. Apr 11, 2009 #1
    1. The problem statement, all variables and given/known data
    I am trying to prove (~P & ~Q) => ~(P V Q) using only MP, negation elimination, &I conjunction, &E simplification, addition, constructive dilemma, biconditional introduction and elimination, conditional proof, and reductio ad absurdum.

    2. Relevant equations

    3. The attempt at a solution
    It seems to me that the only way to do the prove is reductio ad absurdum. But,
    I am stuck after hypothesizing (P V Q). I looked at embedding other hypothesis to get a useful negation but could only come up with ~(P & Q). I don't think it will be useful.

    Any hints on the hypothesis I need to use?
  2. jcsd
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