Disjunction elimination - Definition and Overview

In propositional calculus disjunction elimination is the inference that, if "A or B" is true, and A entails C, and B entails C, then we may justifiably infer C. The reasoning is simple: since at least one of the statements A and B is true, and since either of them would be sufficient to entail C, C is certainly true.

For example, it is true that either I'm inside or I'm outside. It is also true that if I'm inside, I have my wallet on me. It's also true that if I'm outside, I have my wallet on me. Given these three premises, it follows that I have my wallet on me.

Formally:

 ( A ∨ B )
 ( A → C )
 ( B → C )
 ∴ C