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Theorem eqeq12i 2053
Description: A useful inference for substituting definitions into an equality. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 25-May-2011.)
Hypotheses
Ref Expression
eqeq12i.1  |-  A  =  B
eqeq12i.2  |-  C  =  D
Assertion
Ref Expression
eqeq12i  |-  ( A  =  C  <->  B  =  D )

Proof of Theorem eqeq12i
StepHypRef Expression
1 eqeq12i.1 . 2  |-  A  =  B
2 eqeq12i.2 . 2  |-  C  =  D
3 eqeq12 2052 . 2  |-  ( ( A  =  B  /\  C  =  D )  ->  ( A  =  C  <-> 
B  =  D ) )
41, 2, 3mp2an 402 1  |-  ( A  =  C  <->  B  =  D )
Colors of variables: wff set class
Syntax hints:    <-> wb 98    = wceq 1243
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-5 1336  ax-gen 1338  ax-4 1400  ax-17 1419  ax-ext 2022
This theorem depends on definitions:  df-bi 110  df-cleq 2033
This theorem is referenced by:  rabbi  2487  sbceqg  2866  preqr2g  3538  preqr2  3540  otth  3979  rncoeq  4605  eqfnov  5607  mpt22eqb  5610  f1o2ndf1  5849  ecopovsym  6202  sq11i  9343
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