Falsity (Bottom) Introduction
   
 

This rule can be used forwards or backwards to produce a bottom (falsity) formula.

To use it forwards:
  1. select both an empty line and Bottom (falsity) Introduction.

  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.

To use it backwards:
  1. select both a goal line (a bottom formula) and Bottom (falsity) Introduction.

  2. then select the line you wish to use for the rule.

  3. a new goal is added to a proof which is the compliment of the selected formula (if you select ¬X then X is the new goal line and if you select Y then ¬Y is the goal line).