Double Negation/Double Negation Introduction/Proof Rule/Tableau Form

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Proof Rule

Let $\phi$ be a well-formed formula in a tableau proof.

Double Negation Introduction is invoked for $\phi$ as follows:

Pool:    The pooled assumptions of $\phi$      
Formula:    $\neg \neg \phi$      
Description:    Double Negation Introduction      
Depends on:    The line containing the instance of $\phi$      
Abbreviation:    $\text{DNI}$ or $\neg \neg \II$