Metamath Proof Explorer


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 )