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Theorem ssuncl 42871
Description: The class of all subsets of a class is closed under binary union. (Contributed by RP, 3-Jan-2020.)
Hypothesis
Ref Expression
ssficl.a 𝐴 = {𝑧𝑧𝐵}
Assertion
Ref Expression
ssuncl 𝑥𝐴𝑦𝐴 (𝑥𝑦) ∈ 𝐴
Distinct variable groups:   𝑥,𝑦,𝑧   𝑦,𝐴   𝑧,𝐵
Allowed substitution hints:   𝐴(𝑥,𝑧)   𝐵(𝑥,𝑦)

Proof of Theorem ssuncl
StepHypRef Expression
1 ssficl.a . 2 𝐴 = {𝑧𝑧𝐵}
2 vex 3470 . . 3 𝑥 ∈ V
3 vex 3470 . . 3 𝑦 ∈ V
42, 3unex 7727 . 2 (𝑥𝑦) ∈ V
5 sseq1 4000 . 2 (𝑧 = (𝑥𝑦) → (𝑧𝐵 ↔ (𝑥𝑦) ⊆ 𝐵))
6 sseq1 4000 . 2 (𝑧 = 𝑥 → (𝑧𝐵𝑥𝐵))
7 sseq1 4000 . 2 (𝑧 = 𝑦 → (𝑧𝐵𝑦𝐵))
8 unss 4177 . . 3 ((𝑥𝐵𝑦𝐵) ↔ (𝑥𝑦) ⊆ 𝐵)
98biimpi 215 . 2 ((𝑥𝐵𝑦𝐵) → (𝑥𝑦) ⊆ 𝐵)
101, 4, 5, 6, 7, 9cllem0 42867 1 𝑥𝐴𝑦𝐴 (𝑥𝑦) ∈ 𝐴
Colors of variables: wff setvar class
Syntax hints:  wa 395   = wceq 1533  wcel 2098  {cab 2701  wral 3053  Vcvv 3466  cun 3939  wss 3941
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1789  ax-4 1803  ax-5 1905  ax-6 1963  ax-7 2003  ax-8 2100  ax-9 2108  ax-ext 2695  ax-sep 5290  ax-nul 5297  ax-pr 5418  ax-un 7719
This theorem depends on definitions:  df-bi 206  df-an 396  df-or 845  df-tru 1536  df-fal 1546  df-ex 1774  df-sb 2060  df-clab 2702  df-cleq 2716  df-clel 2802  df-ral 3054  df-v 3468  df-dif 3944  df-un 3946  df-in 3948  df-ss 3958  df-nul 4316  df-sn 4622  df-pr 4624  df-uni 4901
This theorem is referenced by: (None)
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