Theorem Proof: Philosophy Forums

Theorem Proof

thefuturism
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Posted 11/13/08 - 11:51 AM: Subject: Theorem Proof	#1
I am trying to prove the theorem: A ≡ ~~A I am only allowed to use the basic SD rules in doing so. I think I have the proof done correctly, but I am unsure if I can assume that " ~~A " is equal to " A " in my proof... or to be more specific: If I am allowed to use " ~~~A " against " A " as a direct contradiction in my negation elimination ( ~E ). Any help would be appreciated. I only ask because I am limited to SD and there are no rules to convert " ~~A " to " A ".

umtigerblue
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Posted 11/25/08 - 02:35 PM:	#2
Try using ~I instead of ~E. Your contradiction should be betwen A and ~A, then use ~I on ~A giving you ~~A.

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