Double Negation/Double Negation Introduction/Sequent Form/Formulation 2

Theorem

 * $\vdash p \implies \neg \neg p$

Proof

 * align="right" | 2 ||
 * align="right" | 1
 * $\neg \neg p$
 * $\neg \neg \mathcal I$
 * 1
 * using formulation 1 of this result
 * using formulation 1 of this result