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Theorem sbeqal1 27608
Description: If  x  =  y always implies  x  =  z, then 
y  =  z is true. (Contributed by Andrew Salmon, 2-Jun-2011.)
Assertion
Ref Expression
sbeqal1  |-  ( A. x ( x  =  y  ->  x  =  z )  ->  y  =  z )
Distinct variable group:    x, z

Proof of Theorem sbeqal1
StepHypRef Expression
1 sb2 1965 . 2  |-  ( A. x ( x  =  y  ->  x  =  z )  ->  [ y  /  x ] x  =  z )
2 equsb3 2043 . 2  |-  ( [ y  /  x ]
x  =  z  <->  y  =  z )
31, 2sylib 188 1  |-  ( A. x ( x  =  y  ->  x  =  z )  ->  y  =  z )
Colors of variables: wff set class
Syntax hints:    -> wi 4   A.wal 1529    = wceq 1625   [wsb 1631
This theorem is referenced by:  sbeqal1i  27609  sbeqalbi  27611
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1535  ax-5 1546  ax-17 1605  ax-9 1637  ax-8 1645  ax-6 1705  ax-7 1710  ax-11 1717  ax-12 1868
This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-tru 1310  df-ex 1531  df-nf 1534  df-sb 1632
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