Conjunction Equivalent to Negation of Implication of Negative/Formulation 1/Reverse Implication

Theorem

 * $\neg \left({p \implies \neg q}\right) \vdash p \land q$

Proofs
By the tableau method of natural deduction:

This proof depends (indirectly) on the Law of the Excluded Middle.

Thus it is not valid in intuitionist logic.