Metamath Proof Explorer

Theorem exbi

Description: Theorem 19.18 of Margaris p. 90. (Contributed by NM, 12-Mar-1993)

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

Proof

Step Hyp Ref Expression
1 id 
 |-  ( ( ph <-> ps ) -> ( ph <-> ps ) )
2 1 alexbii 
 |-  ( A. x ( ph <-> ps ) -> ( E. x ph <-> E. x ps ) )