Metamath Proof Explorer

Theorem pm10.253

Description: Theorem *10.253 in WhiteheadRussell p. 149. (Contributed by Andrew Salmon, 17-Jun-2011)

Ref Expression
Assertion pm10.253 
|- ( -. A. x ph <-> E. x -. ph )

Proof

Step Hyp Ref Expression
1 alex 
 |-  ( A. x ph <-> -. E. x -. ph )
2 1 bicomi 
 |-  ( -. E. x -. ph <-> A. x ph )
3 2 con1bii 
 |-  ( -. A. x ph <-> E. x -. ph )