Theorem pm11.7

Description: Theorem *11.7 in WhiteheadRussell p. 166. (Contributed by Andrew Salmon, 24-May-2011)

	Ref	Expression
Assertion	pm11.7	$$⊢\exists x\exists y\left(\phi \vee \phi \right)\leftrightarrow \exists x\exists y\phi$$

Proof

Step	Hyp	Ref	Expression
1		oridm	$$⊢\left(\phi \vee \phi \right)\leftrightarrow \phi$$
2	1	2exbii	$$⊢\exists x\exists y\left(\phi \vee \phi \right)\leftrightarrow \exists x\exists y\phi$$