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I am having trouble solving this proof. Line 5 is wrong, I know it's Demorgan's Law, but the proof machine doesn't accept that as an answer. I think it only accepts ~Elim, vElim, vIntro, ~Intro, &Intro, etc.enter image description here

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  • Try using ~~P and ~~Q in 5. I think you are doing too much in one step by directly turning ~~P into P.
    – kutschkem
    Oct 10, 2022 at 7:10
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    Disjunction Elim on the first premise: derive P in both cases.
    – Mauro ALLEGRANZA
    Oct 10, 2022 at 8:38

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