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Theorem bj-0eltag 33290
 Description: The empty set belongs to the tagging of a class. (Contributed by BJ, 6-Apr-2019.)
Assertion
Ref Expression
bj-0eltag ∅ ∈ tag 𝐴

Proof of Theorem bj-0eltag
StepHypRef Expression
1 0ex 4942 . . . . 5 ∅ ∈ V
21snid 4353 . . . 4 ∅ ∈ {∅}
32olci 405 . . 3 (∅ ∈ sngl 𝐴 ∨ ∅ ∈ {∅})
4 elun 3896 . . 3 (∅ ∈ (sngl 𝐴 ∪ {∅}) ↔ (∅ ∈ sngl 𝐴 ∨ ∅ ∈ {∅}))
53, 4mpbir 221 . 2 ∅ ∈ (sngl 𝐴 ∪ {∅})
6 df-bj-tag 33287 . 2 tag 𝐴 = (sngl 𝐴 ∪ {∅})
75, 6eleqtrri 2838 1 ∅ ∈ tag 𝐴
 Colors of variables: wff setvar class Syntax hints:   ∨ wo 382   ∈ wcel 2139   ∪ cun 3713  ∅c0 4058  {csn 4321  sngl bj-csngl 33277  tag bj-ctag 33286 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1871  ax-4 1886  ax-5 1988  ax-6 2054  ax-7 2090  ax-9 2148  ax-10 2168  ax-11 2183  ax-12 2196  ax-13 2391  ax-ext 2740  ax-nul 4941 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-tru 1635  df-ex 1854  df-nf 1859  df-sb 2047  df-clab 2747  df-cleq 2753  df-clel 2756  df-nfc 2891  df-v 3342  df-dif 3718  df-un 3720  df-nul 4059  df-sn 4322  df-bj-tag 33287 This theorem is referenced by:  bj-tagn0  33291
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