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Theorem sssnr 3603
Description: Empty set and the singleton itself are subsets of a singleton. Concerning the converse, see exmidsssn 4040. (Contributed by Jim Kingdon, 10-Aug-2018.)
Assertion
Ref Expression
sssnr  |-  ( ( A  =  (/)  \/  A  =  { B } )  ->  A  C_  { B } )

Proof of Theorem sssnr
StepHypRef Expression
1 0ss 3325 . . 3  |-  (/)  C_  { B }
2 sseq1 3048 . . 3  |-  ( A  =  (/)  ->  ( A 
C_  { B }  <->  (/)  C_ 
{ B } ) )
31, 2mpbiri 167 . 2  |-  ( A  =  (/)  ->  A  C_  { B } )
4 eqimss 3079 . 2  |-  ( A  =  { B }  ->  A  C_  { B } )
53, 4jaoi 672 1  |-  ( ( A  =  (/)  \/  A  =  { B } )  ->  A  C_  { B } )
Colors of variables: wff set class
Syntax hints:    -> wi 4    \/ wo 665    = wceq 1290    C_ wss 3000   (/)c0 3287   {csn 3450
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 580  ax-in2 581  ax-io 666  ax-5 1382  ax-7 1383  ax-gen 1384  ax-ie1 1428  ax-ie2 1429  ax-8 1441  ax-10 1442  ax-11 1443  ax-i12 1444  ax-bndl 1445  ax-4 1446  ax-17 1465  ax-i9 1469  ax-ial 1473  ax-i5r 1474  ax-ext 2071
This theorem depends on definitions:  df-bi 116  df-tru 1293  df-nf 1396  df-sb 1694  df-clab 2076  df-cleq 2082  df-clel 2085  df-nfc 2218  df-v 2622  df-dif 3002  df-in 3006  df-ss 3013  df-nul 3288
This theorem is referenced by:  pwsnss  3653
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