Theorem 2exnexn

Description: Theorem *11.51 in WhiteheadRussell p. 164. (Contributed by Andrew Salmon, 24-May-2011) (Proof shortened by Wolf Lammen, 25-Sep-2014)

	Ref	Expression
Assertion	2exnexn	|- ( E. x A. y ph <-> -. A. x E. y -. ph )

Proof

Step	Hyp	Ref	Expression
1		alexn	|- ( A. x E. y -. ph <-> -. E. x A. y ph )
2	1	con2bii	|- ( E. x A. y ph <-> -. A. x E. y -. ph )