Metamath Proof Explorer

Theorem bj-biexex

Description: When ph is substituted for ps , both sides express a form of nonfreeness. (Contributed by BJ, 20-Oct-2019)

Ref Expression
Assertion bj-biexex 
|- ( A. x ( ph -> E. x ps ) <-> ( E. x ph -> E. x ps ) )

Proof

Step Hyp Ref Expression
1 nfe1 
 |-  F/ x E. x ps
2 1 19.23 
 |-  ( A. x ( ph -> E. x ps ) <-> ( E. x ph -> E. x ps ) )