Metamath Proof Explorer

Theorem pm10.252

Description: Theorem *10.252 in WhiteheadRussell p. 149. (Contributed by Andrew Salmon, 17-Jun-2011) (New usage is discouraged.)

Ref Expression
Assertion pm10.252 
|- ( -. E. x ph <-> A. x -. ph )

Proof

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