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Theorem ax9o 1892
Description: Show that the original axiom ax-9o 2080 can be derived from ax9 1891 and others. See ax9from9o 2089 for the rederivation of ax9 1891 from ax-9o 2080.

Normally, ax9o 1892 should be used rather than ax-9o 2080, except by theorems specifically studying the latter's properties. (Contributed by NM, 5-Aug-1993.) (Proof modification is discouraged.)

Assertion
Ref Expression
ax9o  |-  ( A. x ( x  =  y  ->  A. x ph )  ->  ph )

Proof of Theorem ax9o
StepHypRef Expression
1 ax9 1891 . . 3  |-  -.  A. x  -.  x  =  y
2 con3 126 . . . 4  |-  ( ( x  =  y  ->  A. x ph )  -> 
( -.  A. x ph  ->  -.  x  =  y ) )
32al2imi 1548 . . 3  |-  ( A. x ( x  =  y  ->  A. x ph )  ->  ( A. x  -.  A. x ph  ->  A. x  -.  x  =  y ) )
41, 3mtoi 169 . 2  |-  ( A. x ( x  =  y  ->  A. x ph )  ->  -.  A. x  -.  A. x ph )
5 ax6o 1725 . 2  |-  ( -. 
A. x  -.  A. x ph  ->  ph )
64, 5syl 15 1  |-  ( A. x ( x  =  y  ->  A. x ph )  ->  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4   A.wal 1527
This theorem is referenced by:  equsal  1903  spimt  1917  cbv1h  1921
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1533  ax-5 1544  ax-17 1603  ax-9 1636  ax-8 1644  ax-6 1704  ax-7 1709  ax-11 1716  ax-12 1868
This theorem depends on definitions:  df-bi 177  df-an 360  df-ex 1529
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