Theorem snss 3808

Description: The singleton of an element of a class is a subset of the class (inference form of snssg 3807). Theorem 7.4 of [Quine] p. 49. (Contributed by NM, 21-Jun-1993.) (Proof shortened by BJ, 1-Jan-2025.)

Hypothesis

Ref	Expression
snss.1	|- A e. _V

Assertion

Ref	Expression
snss	|- ( A e. B <-> { A } C_ B )

Proof of Theorem snss

Step	Hyp	Ref	Expression
1		snss.1	. 2 |- A e. _V
2		snssg 3807	. 2 |- ( A e. _V -> ( A e. B <-> { A } C_ B ) )
3	1, 2	ax-mp 5	1 |- ( A e. B <-> { A } C_ B )

Syntax hints:   <-> wb 105   e. wcel 2202   _Vcvv 2802   C_ wss 3200   {csn 3669

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 716  ax-5 1495  ax-7 1496  ax-gen 1497  ax-ie1 1541  ax-ie2 1542  ax-8 1552  ax-10 1553  ax-11 1554  ax-i12 1555  ax-bndl 1557  ax-4 1558  ax-17 1574  ax-i9 1578  ax-ial 1582  ax-i5r 1583  ax-ext 2213

This theorem depends on definitions:  df-bi 117  df-tru 1400  df-nf 1509  df-sb 1811  df-clab 2218  df-cleq 2224  df-clel 2227  df-nfc 2363  df-v 2804  df-in 3206  df-ss 3213  df-sn 3675

This theorem is referenced by:  snssgOLD  3809  prss  3829  tpss  3841  snelpw  4304  sspwb  4308  mss  4318  exss  4319  reg2exmidlema  4632  elomssom  4703  relsn  4831  fnressn  5840  un0mulcl  9436  nn0ssz  9497  fimaxre2  11805  fsum2dlemstep  12013  fsumabs  12044  fsumiun  12056  fprod2dlemstep  12201  dvmptfsum  15468  elply2  15478  elplyd  15484  ply1term  15486  plymullem  15493  bdsnss  16519