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Theorem sb6rf 1833
Description: Reversed substitution. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.)
Hypothesis
Ref Expression
sb5rf.1  |-  ( ph  ->  A. y ph )
Assertion
Ref Expression
sb6rf  |-  ( ph  <->  A. y ( y  =  x  ->  [ y  /  x ] ph )
)

Proof of Theorem sb6rf
StepHypRef Expression
1 sb5rf.1 . . 3  |-  ( ph  ->  A. y ph )
2 sbequ1 1748 . . . . 5  |-  ( x  =  y  ->  ( ph  ->  [ y  /  x ] ph ) )
32equcoms 1688 . . . 4  |-  ( y  =  x  ->  ( ph  ->  [ y  /  x ] ph ) )
43com12 30 . . 3  |-  ( ph  ->  ( y  =  x  ->  [ y  /  x ] ph ) )
51, 4alrimih 1449 . 2  |-  ( ph  ->  A. y ( y  =  x  ->  [ y  /  x ] ph ) )
6 sb2 1747 . . 3  |-  ( A. y ( y  =  x  ->  [ y  /  x ] ph )  ->  [ x  /  y ] [ y  /  x ] ph )
71sbid2h 1829 . . 3  |-  ( [ x  /  y ] [ y  /  x ] ph  <->  ph )
86, 7sylib 121 . 2  |-  ( A. y ( y  =  x  ->  [ y  /  x ] ph )  ->  ph )
95, 8impbii 125 1  |-  ( ph  <->  A. y ( y  =  x  ->  [ y  /  x ] ph )
)
Colors of variables: wff set class
Syntax hints:    -> wi 4    <-> wb 104   A.wal 1333   [wsb 1742
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-5 1427  ax-gen 1429  ax-ie1 1473  ax-ie2 1474  ax-8 1484  ax-11 1486  ax-4 1490  ax-17 1506  ax-i9 1510  ax-ial 1514
This theorem depends on definitions:  df-bi 116  df-sb 1743
This theorem is referenced by:  2sb6rf  1970  eu1  2031
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