Proof of double negation elimination using natural deduction

logicnatural-deduction

I am trying to prove that $\neg A \to \bot \vdash A$, I can only use double negation elimination to get the conclusion, but I don't know how to prove double negation elimination.

Below is my proof for $\neg A \to \bot \vdash A$:

1 $\neg A\to\bot$

2 $\neg A$ (assumption)

3 $\bot$ ($\to$e 1, 2)

4 $\neg\neg A$ ($\neg$i 2-3)

5 $A$ (DNE 4)

The rules that can be used would be the basic rules of natural deduction:
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Best Answer

The rules you list comprise a natural deduction system for intuitionistic logic. The sequent $\lnot A\to \bot\vdash A$ is not valid in intuitionistic logic, so it is not provable in your system.

To prove $\lnot A\to \bot\vdash A$, you need to be working with a natural deduction system for classical logic, which means adding an additional rule to your system. One common choice is to add double negation elimination itself; this makes your proof a valid one. Other common choices are adding reductio ad absurdum (proof by contradiction) or the law of excluded middle.

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