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Theorem snsssn 4846
Description: If a singleton is a subset of another, their members are equal. (Contributed by NM, 28-May-2006.)
Hypothesis
Ref Expression
sneqr.1 𝐴 ∈ V
Assertion
Ref Expression
snsssn ({𝐴} ⊆ {𝐵} → 𝐴 = 𝐵)

Proof of Theorem snsssn
StepHypRef Expression
1 sssn 4831 . 2 ({𝐴} ⊆ {𝐵} ↔ ({𝐴} = ∅ ∨ {𝐴} = {𝐵}))
2 sneqr.1 . . . . . 6 𝐴 ∈ V
32snnz 4781 . . . . 5 {𝐴} ≠ ∅
43neii 2940 . . . 4 ¬ {𝐴} = ∅
54pm2.21i 119 . . 3 ({𝐴} = ∅ → 𝐴 = 𝐵)
62sneqr 4845 . . 3 ({𝐴} = {𝐵} → 𝐴 = 𝐵)
75, 6jaoi 857 . 2 (({𝐴} = ∅ ∨ {𝐴} = {𝐵}) → 𝐴 = 𝐵)
81, 7sylbi 217 1 ({𝐴} ⊆ {𝐵} → 𝐴 = 𝐵)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wo 847   = wceq 1537  wcel 2106  Vcvv 3478  wss 3963  c0 4339  {csn 4631
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-5 1908  ax-6 1965  ax-7 2005  ax-8 2108  ax-9 2116  ax-ext 2706
This theorem depends on definitions:  df-bi 207  df-an 396  df-or 848  df-tru 1540  df-fal 1550  df-ex 1777  df-sb 2063  df-clab 2713  df-cleq 2727  df-clel 2814  df-ne 2939  df-v 3480  df-dif 3966  df-ss 3980  df-nul 4340  df-sn 4632
This theorem is referenced by:  k0004lem3  44139
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