Double Negation/Double Negation Introduction/Sequent Form/Formulation 1

Theorem
If we can conclude $p$, then we may infer $\neg \neg p$:


 * $p \vdash \neg \neg p$

where $\neg$ denotes the negation operator.

It can be written:
 * $\displaystyle {p \over \neg \neg p} \neg \neg_i$

This is called the Law of Double Negation Introduction

Its abbreviation in a tableau proof is $\neg \neg \mathcal I$.

Proof
By the tableau method of natural deduction: