Reductio ad Absurdum/Variant 1/Proof 1

Theorem

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

Proof
By the tableau method of natural deduction:

Comment
It can be seen that this result depends on the rule of Double Negation Elimination.

As this depends on the Law of the Excluded Middle, it invalidates the Reductio Ad Absurdum from the intuitionist system.