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Theorem 3sstr4d 3112
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 3098 . 2  |-  ( ph  ->  ( C  C_  D  <->  A 
C_  B ) )
51, 4mpbird 166 1  |-  ( ph  ->  C  C_  D )
Colors of variables: wff set class
Syntax hints:    -> wi 4    = wceq 1316    C_ wss 3041
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 1408  ax-7 1409  ax-gen 1410  ax-ie1 1454  ax-ie2 1455  ax-8 1467  ax-11 1469  ax-4 1472  ax-17 1491  ax-i9 1495  ax-ial 1499  ax-i5r 1500  ax-ext 2099
This theorem depends on definitions:  df-bi 116  df-nf 1422  df-sb 1721  df-clab 2104  df-cleq 2110  df-clel 2113  df-in 3047  df-ss 3054
This theorem is referenced by:  rdgss  6248  sucinc2  6310  oawordi  6333  nnnninf  6991  fzoss1  9916  fzoss2  9917  clsss  12214  ntrss  12215  sslm  12343  txss12  12362  metss2lem  12593  xmettxlem  12605  xmettx  12606  nnsf  13126  nninfself  13136
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