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Theorem trss 4094
Description: An element of a transitive class is a subset of the class. (Contributed by NM, 7-Aug-1994.)
Assertion
Ref Expression
trss  |-  ( Tr  A  ->  ( B  e.  A  ->  B  C_  A ) )

Proof of Theorem trss
Dummy variable  x is distinct from all other variables.
StepHypRef Expression
1 eleq1 2233 . . . . 5  |-  ( x  =  B  ->  (
x  e.  A  <->  B  e.  A ) )
2 sseq1 3170 . . . . 5  |-  ( x  =  B  ->  (
x  C_  A  <->  B  C_  A
) )
31, 2imbi12d 233 . . . 4  |-  ( x  =  B  ->  (
( x  e.  A  ->  x  C_  A )  <->  ( B  e.  A  ->  B  C_  A ) ) )
43imbi2d 229 . . 3  |-  ( x  =  B  ->  (
( Tr  A  -> 
( x  e.  A  ->  x  C_  A )
)  <->  ( Tr  A  ->  ( B  e.  A  ->  B  C_  A )
) ) )
5 dftr3 4089 . . . 4  |-  ( Tr  A  <->  A. x  e.  A  x  C_  A )
6 rsp 2517 . . . 4  |-  ( A. x  e.  A  x  C_  A  ->  ( x  e.  A  ->  x  C_  A ) )
75, 6sylbi 120 . . 3  |-  ( Tr  A  ->  ( x  e.  A  ->  x  C_  A ) )
84, 7vtoclg 2790 . 2  |-  ( B  e.  A  ->  ( Tr  A  ->  ( B  e.  A  ->  B  C_  A ) ) )
98pm2.43b 52 1  |-  ( Tr  A  ->  ( B  e.  A  ->  B  C_  A ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    = wceq 1348    e. wcel 2141   A.wral 2448    C_ wss 3121   Tr wtr 4085
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-io 704  ax-5 1440  ax-7 1441  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-8 1497  ax-10 1498  ax-11 1499  ax-i12 1500  ax-bndl 1502  ax-4 1503  ax-17 1519  ax-i9 1523  ax-ial 1527  ax-i5r 1528  ax-ext 2152
This theorem depends on definitions:  df-bi 116  df-tru 1351  df-nf 1454  df-sb 1756  df-clab 2157  df-cleq 2163  df-clel 2166  df-nfc 2301  df-ral 2453  df-v 2732  df-in 3127  df-ss 3134  df-uni 3795  df-tr 4086
This theorem is referenced by:  trin  4095  triun  4098  trintssm  4101  tz7.2  4337  ordelss  4362  trsucss  4406  ordsucss  4486  ctinf  12372
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