Double Negation/Double Negation Introduction

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Proof Rule

The rule of double negation introduction is a valid argument in types of logic dealing with negation $\neg$.

This includes propositional logic and predicate logic, and in particular natural deduction.

Proof Rule

If we can conclude $\phi$, then we may infer $\neg \neg \phi$.

Sequent Form

$p \vdash \neg \neg p$