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Theorem sseq12d 3029
Description: An equality deduction for the subclass relationship. (Contributed by NM, 31-May-1999.)
Hypotheses
Ref Expression
sseq1d.1  |-  ( ph  ->  A  =  B )
sseq12d.2  |-  ( ph  ->  C  =  D )
Assertion
Ref Expression
sseq12d  |-  ( ph  ->  ( A  C_  C  <->  B 
C_  D ) )

Proof of Theorem sseq12d
StepHypRef Expression
1 sseq1d.1 . . 3  |-  ( ph  ->  A  =  B )
21sseq1d 3027 . 2  |-  ( ph  ->  ( A  C_  C  <->  B 
C_  C ) )
3 sseq12d.2 . . 3  |-  ( ph  ->  C  =  D )
43sseq2d 3028 . 2  |-  ( ph  ->  ( B  C_  C  <->  B 
C_  D ) )
52, 4bitrd 186 1  |-  ( ph  ->  ( A  C_  C  <->  B 
C_  D ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    <-> wb 103    = wceq 1285    C_ wss 2974
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-5 1377  ax-7 1378  ax-gen 1379  ax-ie1 1423  ax-ie2 1424  ax-8 1436  ax-11 1438  ax-4 1441  ax-17 1460  ax-i9 1464  ax-ial 1468  ax-i5r 1469  ax-ext 2064
This theorem depends on definitions:  df-bi 115  df-nf 1391  df-sb 1687  df-clab 2069  df-cleq 2075  df-clel 2078  df-in 2980  df-ss 2987
This theorem is referenced by:  3sstr3d  3042  3sstr4d  3043  ssdifeq0  3332  relcnvtr  4870  rdgisucinc  6034  oawordriexmid  6114  nnaword  6150  nnawordi  6154
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