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Definition df-bj-tag 33267
Description: Definition of the tagged copy of a class, that is, the adjunction to (an isomorph of) 𝐴 of a disjoint element (here, the empty set). Remark: this could be used for the one-point compactification of a topological space. (Contributed by BJ, 6-Oct-2018.)
Assertion
Ref Expression
df-bj-tag tag 𝐴 = (sngl 𝐴 ∪ {∅})

Detailed syntax breakdown of Definition df-bj-tag
StepHypRef Expression
1 cA . . 3 class 𝐴
21bj-ctag 33266 . 2 class tag 𝐴
31bj-csngl 33257 . . 3 class sngl 𝐴
4 c0 4110 . . . 4 class
54csn 4364 . . 3 class {∅}
63, 5cun 3761 . 2 class (sngl 𝐴 ∪ {∅})
72, 6wceq 1637 1 wff tag 𝐴 = (sngl 𝐴 ∪ {∅})
Colors of variables: wff setvar class
This definition is referenced by:  bj-tageq  33268  bj-eltag  33269  bj-0eltag  33270  bj-tagss  33272  bj-snglsstag  33273  bj-sngltag  33275  bj-tagex  33279
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