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Multiple Choice question about Proposition Logic

  1. Oct 31, 2008 #1
    The question is here: http://dl.getdropbox.com/u/175564/logic.png

    The correct answer is D.

    My attempt to the problem:
    Let the beginnings of the sentences be A.
    In a, A is B -/-> C is D.
    In b, A is B -/-> C is D.
    These first two do not make sense.

    in c and d, the word "only" suggests exaggeration.
    In c, A is B -/-> B must be C.
    In d, A is B -/-> A must be C.

    Still, I am sure thoroughly why d is the correct answer.
    Please, let me know why.
  2. jcsd
  3. Jan 12, 2009 #2
    You need modal logic here, for cannot and mustn't, which are modalities.
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