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Theorem 3sstr4d 3051
Description: Substitution of equality into both sides of a subclass relationship. (Contributed by NM, 30-Nov-1995.) (Proof shortened by Eric Schmidt, 26-Jan-2007.)
Hypotheses
Ref Expression
3sstr4d.1  |-  ( ph  ->  A  C_  B )
3sstr4d.2  |-  ( ph  ->  C  =  A )
3sstr4d.3  |-  ( ph  ->  D  =  B )
Assertion
Ref Expression
3sstr4d  |-  ( ph  ->  C  C_  D )

Proof of Theorem 3sstr4d
StepHypRef Expression
1 3sstr4d.1 . 2  |-  ( ph  ->  A  C_  B )
2 3sstr4d.2 . . 3  |-  ( ph  ->  C  =  A )
3 3sstr4d.3 . . 3  |-  ( ph  ->  D  =  B )
42, 3sseq12d 3037 . 2  |-  ( ph  ->  ( C  C_  D  <->  A 
C_  B ) )
51, 4mpbird 165 1  |-  ( ph  ->  C  C_  D )
Colors of variables: wff set class
Syntax hints:    -> wi 4    = wceq 1285    C_ wss 2982
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 2065
This theorem depends on definitions:  df-bi 115  df-nf 1391  df-sb 1688  df-clab 2070  df-cleq 2076  df-clel 2079  df-in 2988  df-ss 2995
This theorem is referenced by:  rdgss  6052  sucinc2  6110  oawordi  6133  fzoss1  9309  fzoss2  9310
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