Proof by Cases

Sequent
Proof by cases is a valid argument in types of logic dealing with disjunctions $\lor$.

This includes propositional logic and predicate logic, and in particular natural deduction.

Variants
The following forms can be used as variants of this theorem:

Explanation
Thus a disjunction is eliminated from a sequent.

Also see

 * Definition:Disjunction


 * Rule of Addition
 * Principle of Dilemma