Theorem pm11.7

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

	Ref	Expression
Assertion	pm11.7	|- ( E. x E. y ( ph \/ ph ) <-> E. x E. y ph )

Proof

Step	Hyp	Ref	Expression
1		oridm	|- ( ( ph \/ ph ) <-> ph )
2	1	2exbii	|- ( E. x E. y ( ph \/ ph ) <-> E. x E. y ph )