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Theorem elsuc2g 4223
Description: Variant of membership in a successor, requiring that  B rather than  A be a set. (Contributed by NM, 28-Oct-2003.)
Assertion
Ref Expression
elsuc2g  |-  ( B  e.  V  ->  ( A  e.  suc  B  <->  ( A  e.  B  \/  A  =  B ) ) )

Proof of Theorem elsuc2g
StepHypRef Expression
1 df-suc 4189 . . 3  |-  suc  B  =  ( B  u.  { B } )
21eleq2i 2154 . 2  |-  ( A  e.  suc  B  <->  A  e.  ( B  u.  { B } ) )
3 elun 3139 . . 3  |-  ( A  e.  ( B  u.  { B } )  <->  ( A  e.  B  \/  A  e.  { B } ) )
4 elsn2g 3472 . . . 4  |-  ( B  e.  V  ->  ( A  e.  { B } 
<->  A  =  B ) )
54orbi2d 739 . . 3  |-  ( B  e.  V  ->  (
( A  e.  B  \/  A  e.  { B } )  <->  ( A  e.  B  \/  A  =  B ) ) )
63, 5syl5bb 190 . 2  |-  ( B  e.  V  ->  ( A  e.  ( B  u.  { B } )  <-> 
( A  e.  B  \/  A  =  B
) ) )
72, 6syl5bb 190 1  |-  ( B  e.  V  ->  ( A  e.  suc  B  <->  ( A  e.  B  \/  A  =  B ) ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    <-> wb 103    \/ wo 664    = wceq 1289    e. wcel 1438    u. cun 2995   {csn 3441   suc csuc 4183
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-io 665  ax-5 1381  ax-7 1382  ax-gen 1383  ax-ie1 1427  ax-ie2 1428  ax-8 1440  ax-10 1441  ax-11 1442  ax-i12 1443  ax-bndl 1444  ax-4 1445  ax-17 1464  ax-i9 1468  ax-ial 1472  ax-i5r 1473  ax-ext 2070
This theorem depends on definitions:  df-bi 115  df-tru 1292  df-nf 1395  df-sb 1693  df-clab 2075  df-cleq 2081  df-clel 2084  df-nfc 2217  df-v 2621  df-un 3001  df-sn 3447  df-suc 4189
This theorem is referenced by:  elsuc2  4225  nntri3or  6236  frec2uzltd  9775
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