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Theorem ax9v2 1916
Description: Second of two weakened versions of ax9v 1914, with an extra dv condition on  y ,  z see comments there. (Contributed by BJ, 7-Dec-2020.)
Assertion
Ref Expression
ax9v2  |-  ( x  =  y  ->  (
z  e.  x  -> 
z  e.  y ) )
Distinct variable groups:    x, y    y, z

Proof of Theorem ax9v2
StepHypRef Expression
1 ax9v 1914 1  |-  ( x  =  y  ->  (
z  e.  x  -> 
z  e.  y ) )
Colors of variables: wff setvar class
Syntax hints:    -> wi 4
This theorem was proved from axioms:  ax-9 1913
This theorem is referenced by:  ax9  1917
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