๐ฎโโ๏ธ Proof by case distinction
= If the assumption from A leads us to B, and if the assumption from ยฌA also leads us to B, then we may infer B, and the assumptions A and ยฌA can both be eliminated.
Notation
(FU) \frac{\begin{array} & {[A]_{i}} \\ \vdots \\ B \end{array} \quad \begin{array} & {[\neg A]_{i}} \\ \vdots \\ B \end{array}}{B}i