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Theorem sssnr 3498
 Description: Empty set and the singleton itself are subsets of a singleton. (Contributed by Jim Kingdon, 10-Aug-2018.)
Assertion
Ref Expression
sssnr ((A = ∅ A = {B}) → A ⊆ {B})

Proof of Theorem sssnr
StepHypRef Expression
1 0ss 3232 . . 3 ∅ ⊆ {B}
2 sseq1 2943 . . 3 (A = ∅ → (A ⊆ {B} ↔ ∅ ⊆ {B}))
31, 2mpbiri 157 . 2 (A = ∅ → A ⊆ {B})
4 eqimss 2974 . 2 (A = {B} → A ⊆ {B})
53, 4jaoi 623 1 ((A = ∅ A = {B}) → A ⊆ {B})
 Colors of variables: wff set class Syntax hints:   → wi 4   ∨ wo 616   = wceq 1228   ⊆ wss 2894  ∅c0 3201  {csn 3350 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 532  ax-in2 533  ax-io 617  ax-5 1316  ax-7 1317  ax-gen 1318  ax-ie1 1363  ax-ie2 1364  ax-8 1376  ax-10 1377  ax-11 1378  ax-i12 1379  ax-bnd 1380  ax-4 1381  ax-17 1400  ax-i9 1404  ax-ial 1409  ax-i5r 1410  ax-ext 2004 This theorem depends on definitions:  df-bi 110  df-tru 1231  df-nf 1330  df-sb 1628  df-clab 2009  df-cleq 2015  df-clel 2018  df-nfc 2149  df-v 2537  df-dif 2897  df-in 2901  df-ss 2908  df-nul 3202 This theorem is referenced by:  pwsnss  3548
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