Theorem snidb 3663

Description: A class is a set iff it is a member of its singleton. (Contributed by NM, 5-Apr-2004.)

Assertion

Ref	Expression
snidb	|- ( A e. _V <-> A e. { A } )

Proof of Theorem snidb

Step	Hyp	Ref	Expression
1		snidg 3662	. 2 |- ( A e. _V -> A e. { A } )
2		elex 2783	. 2 |- ( A e. { A } -> A e. _V )
3	1, 2	impbii 126	1 |- ( A e. _V <-> A e. { A } )

Syntax hints:   <-> wb 105   e. wcel 2176   _Vcvv 2772   {csn 3633

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 711  ax-5 1470  ax-7 1471  ax-gen 1472  ax-ie1 1516  ax-ie2 1517  ax-8 1527  ax-10 1528  ax-11 1529  ax-i12 1530  ax-bndl 1532  ax-4 1533  ax-17 1549  ax-i9 1553  ax-ial 1557  ax-i5r 1558  ax-ext 2187

This theorem depends on definitions:  df-bi 117  df-tru 1376  df-nf 1484  df-sb 1786  df-clab 2192  df-cleq 2198  df-clel 2201  df-nfc 2337  df-v 2774  df-sn 3639

This theorem is referenced by:  snid  3664