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Theorem ax11a2 1743
Description: Derive ax-11o 1745 from a hypothesis in the form of ax-11 1438. The hypothesis is even weaker than ax-11 1438, with  z both distinct from  x and not occurring in  ph. Thus the hypothesis provides an alternate axiom that can be used in place of ax11o 1744. (Contributed by NM, 2-Feb-2007.)
Hypothesis
Ref Expression
ax11a2.1  |-  ( x  =  z  ->  ( A. z ph  ->  A. x
( x  =  z  ->  ph ) ) )
Assertion
Ref Expression
ax11a2  |-  ( -. 
A. x  x  =  y  ->  ( x  =  y  ->  ( ph  ->  A. x ( x  =  y  ->  ph )
) ) )
Distinct variable groups:    x, z    y,
z    ph, z
Allowed substitution hints:    ph( x, y)

Proof of Theorem ax11a2
StepHypRef Expression
1 ax-17 1460 . . 3  |-  ( ph  ->  A. z ph )
2 ax11a2.1 . . 3  |-  ( x  =  z  ->  ( A. z ph  ->  A. x
( x  =  z  ->  ph ) ) )
31, 2syl5 32 . 2  |-  ( x  =  z  ->  ( ph  ->  A. x ( x  =  z  ->  ph )
) )
43ax11v2 1742 1  |-  ( -. 
A. x  x  =  y  ->  ( x  =  y  ->  ( ph  ->  A. x ( x  =  y  ->  ph )
) ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4   A.wal 1283
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-in2 578  ax-io 663  ax-5 1377  ax-7 1378  ax-gen 1379  ax-ie1 1423  ax-ie2 1424  ax-8 1436  ax-10 1437  ax-11 1438  ax-i12 1439  ax-4 1441  ax-17 1460  ax-i9 1464  ax-ial 1468
This theorem depends on definitions:  df-bi 115  df-nf 1391  df-sb 1687
This theorem is referenced by:  ax11o  1744
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