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Help with indirect logic proof please!

  1. Mar 28, 2012 #1
    Using the five axioms below prove: p→q

    A1: p→~y
    A2: ~r→q
    A3: p→~z
    A4: x→ q or z
    A5: r→x or y

    Do I have to take the contrapositive of some of the axioms to begin this proof?
  2. jcsd
  3. Mar 29, 2012 #2


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    Not necessarily.
    You can also solve it using the tautology (r or ~r) and using or-elimination (i.e. assuming p, show that r -> q and ~r -> q).
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