# Rule of Idempotence/Disjunction

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## Theorem

### Formulation 1

$p \dashv \vdash p \lor p$

### Formulation 2

$\vdash p \iff \paren {p \lor p}$

Its abbreviation in a tableau proof is $\textrm{Idemp}$.

## Also known as

This rule is also known as the law of tautology for logical addition (or disjunction).