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Theorem 3eltr4i 2375
Description: Substitution of equal classes into membership relation. (Contributed by Mario Carneiro, 6-Jan-2017.)
Hypotheses
Ref Expression
3eltr4.1  |-  A  e.  B
3eltr4.2  |-  C  =  A
3eltr4.3  |-  D  =  B
Assertion
Ref Expression
3eltr4i  |-  C  e.  D

Proof of Theorem 3eltr4i
StepHypRef Expression
1 3eltr4.2 . 2  |-  C  =  A
2 3eltr4.1 . . 3  |-  A  e.  B
3 3eltr4.3 . . 3  |-  D  =  B
42, 3eleqtrri 2369 . 2  |-  A  e.  D
51, 4eqeltri 2366 1  |-  C  e.  D
Colors of variables: wff set class
Syntax hints:    = wceq 1632    e. wcel 1696
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1536  ax-5 1547  ax-17 1606  ax-9 1644  ax-8 1661  ax-11 1727  ax-ext 2277
This theorem depends on definitions:  df-bi 177  df-an 360  df-ex 1532  df-cleq 2289  df-clel 2292
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