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Theorem ax13 1996
Description: Derive ax-13 1944 from ax13v 1945 via axc9 1995. This shows that the weakening in ax13v 1945 is still sufficient for a complete system. (Contributed by NM, 21-Dec-2015.) (Proof shortened by Wolf Lammen, 31-Jan-2018.)
Assertion
Ref Expression
ax13  |-  ( -.  x  =  y  -> 
( y  =  z  ->  A. x  y  =  z ) )

Proof of Theorem ax13
StepHypRef Expression
1 sp 1795 . . . 4  |-  ( A. x  x  =  y  ->  x  =  y )
21con3i 135 . . 3  |-  ( -.  x  =  y  ->  -.  A. x  x  =  y )
3 sp 1795 . . . 4  |-  ( A. x  x  =  z  ->  x  =  z )
43con3i 135 . . 3  |-  ( -.  x  =  z  ->  -.  A. x  x  =  z )
5 axc9 1995 . . 3  |-  ( -. 
A. x  x  =  y  ->  ( -.  A. x  x  =  z  ->  ( y  =  z  ->  A. x  y  =  z )
) )
62, 4, 5syl2im 38 . 2  |-  ( -.  x  =  y  -> 
( -.  x  =  z  ->  ( y  =  z  ->  A. x  y  =  z )
) )
7 ax13b 1744 . 2  |-  ( ( -.  x  =  y  ->  ( y  =  z  ->  A. x  y  =  z )
)  <->  ( -.  x  =  y  ->  ( -.  x  =  z  -> 
( y  =  z  ->  A. x  y  =  z ) ) ) )
86, 7mpbir 209 1  |-  ( -.  x  =  y  -> 
( y  =  z  ->  A. x  y  =  z ) )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    -> wi 4   A.wal 1368
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1592  ax-4 1603  ax-5 1671  ax-6 1709  ax-7 1729  ax-10 1776  ax-12 1793  ax-13 1944
This theorem depends on definitions:  df-bi 185  df-an 371  df-ex 1588  df-nf 1591
This theorem is referenced by:  equvini  2043  sbequi  2072
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