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Definition df-rank 8878
Description: Define the rank function. See rankval 8929, rankval2 8931, rankval3 8953, or rankval4 8980 its value. The rank is a kind of "inverse" of the cumulative hierarchy of sets function 𝑅1: given a set, it returns an ordinal number telling us the smallest layer of the hierarchy to which the set belongs. Based on Definition 9.14 of [TakeutiZaring] p. 79. Theorem rankid 8946 illustrates the "inverse" concept. Another nice theorem showing the relationship is rankr1a 8949. (Contributed by NM, 11-Oct-2003.)
Assertion
Ref Expression
df-rank rank = (𝑥 ∈ V ↦ {𝑦 ∈ On ∣ 𝑥 ∈ (𝑅1‘suc 𝑦)})
Distinct variable group:   𝑥,𝑦

Detailed syntax breakdown of Definition df-rank
StepHypRef Expression
1 crnk 8876 . 2 class rank
2 vx . . 3 setvar 𝑥
3 cvv 3398 . . 3 class V
42cv 1636 . . . . . 6 class 𝑥
5 vy . . . . . . . . 9 setvar 𝑦
65cv 1636 . . . . . . . 8 class 𝑦
76csuc 5945 . . . . . . 7 class suc 𝑦
8 cr1 8875 . . . . . . 7 class 𝑅1
97, 8cfv 6104 . . . . . 6 class (𝑅1‘suc 𝑦)
104, 9wcel 2157 . . . . 5 wff 𝑥 ∈ (𝑅1‘suc 𝑦)
11 con0 5943 . . . . 5 class On
1210, 5, 11crab 3107 . . . 4 class {𝑦 ∈ On ∣ 𝑥 ∈ (𝑅1‘suc 𝑦)}
1312cint 4676 . . 3 class {𝑦 ∈ On ∣ 𝑥 ∈ (𝑅1‘suc 𝑦)}
142, 3, 13cmpt 4930 . 2 class (𝑥 ∈ V ↦ {𝑦 ∈ On ∣ 𝑥 ∈ (𝑅1‘suc 𝑦)})
151, 14wceq 1637 1 wff rank = (𝑥 ∈ V ↦ {𝑦 ∈ On ∣ 𝑥 ∈ (𝑅1‘suc 𝑦)})
Colors of variables: wff setvar class
This definition is referenced by:  rankf  8907  rankvalb  8910
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