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Definition df-ndx 15640
Description: Define the structure component index extractor. See theorem ndxarg 15657 to understand its purpose. The restriction to allows ndx to exist as a set, since I is a proper class. In principle, we could have chosen or (if we revise all structure component definitions such as df-base 15642) another set such as the natural ordinal numbers ω (df-om 6931). (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 15634 . 2 class ndx
2 cid 4934 . . 3 class I
3 cn 10863 . . 3 class
42, 3cres 5026 . 2 class ( I ↾ ℕ)
51, 4wceq 1474 1 wff ndx = ( I ↾ ℕ)
Colors of variables: wff setvar class
This definition is referenced by:  wunndx  15653  ndxarg  15657
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