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Definition df-ndx 16481
 Description: Define the structure component index extractor. See theorem ndxarg 16503 to understand its purpose. The restriction to ℕ ensures that ndx is a set. The restriction to some set is necessary since I is a proper class. In principle, we could have chosen ℂ or (if we revise all structure component definitions such as df-base 16484) another set such as the set of finite ordinals ω (df-om 7564). (Contributed by NM, 4-Sep-2011.)
Assertion
Ref Expression
df-ndx ndx = ( I ↾ ℕ)

Detailed syntax breakdown of Definition df-ndx
StepHypRef Expression
1 cnx 16475 . 2 class ndx
2 cid 5425 . . 3 class I
3 cn 11628 . . 3 class
42, 3cres 5522 . 2 class ( I ↾ ℕ)
51, 4wceq 1538 1 wff ndx = ( I ↾ ℕ)
 Colors of variables: wff setvar class This definition is referenced by:  wunndx  16499  ndxarg  16503  bj-ndxarg  34511
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