This rule can be used forwards to derive bottom from two contradictory lines from a bottom goal line and another formula.
Note: Not Elimination is the same rule as Bottom Introduction

1. select both an empty line and Not Elimination.
2. then select two contradictory formulae (for example p and ¬p) in the scope of the empty line.
3. a new bottom goal line will be added to your proof.

1. select both a goal line (a bottom formula) and Not Elimination.
2. then select a negated formula which is in the scope of the goal line.
3. the complement of the formula selected will then be added as a new goal in your proof.