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Definition df-ndx 13146
Description: Define the structure component index extractor. See theorem ndxarg 13163 to understand its purpose. The restriction to  NN allows  ndx to exist as a set, since  _I is a proper class. In principle, we could have chosen  CC or (if we revise all structure component definitions such as df-base 13148) another set such as the natural ordinal numbers  om (df-om 4657). (Contributed by NM, 4-Sep-2011.)
Assertion
Ref Expression
df-ndx  |-  ndx  =  (  _I  |`  NN )

Detailed syntax breakdown of Definition df-ndx
StepHypRef Expression
1 cnx 13140 . 2  class  ndx
2 cid 4304 . . 3  class  _I
3 cn 9742 . . 3  class  NN
42, 3cres 4691 . 2  class  (  _I  |`  NN )
51, 4wceq 1624 1  wff  ndx  =  (  _I  |`  NN )
Colors of variables: wff set class
This definition is referenced by:  wunndx  13159  ndxarg  13163
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