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Definition df-bj-tag 32770
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  u.  { (/)
} )

Detailed syntax breakdown of Definition df-bj-tag
StepHypRef Expression
1 cA . . 3  class  A
21bj-ctag 32769 . 2  class tag  A
31bj-csngl 32760 . . 3  class sngl  A
4 c0 3737 . . . 4  class  (/)
54csn 3977 . . 3  class  { (/) }
63, 5cun 3426 . 2  class  (sngl  A  u.  { (/) } )
72, 6wceq 1370 1  wff tag  A  =  (sngl  A  u.  { (/)
} )
Colors of variables: wff setvar class
This definition is referenced by:  bj-tageq  32771  bj-eltag  32772  bj-0eltag  32773  bj-tagss  32775  bj-snglsstag  32776  bj-sngltag  32778  bj-tagex  32782
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