Metamath Proof Explorer


Definition df-r1

Description: Define the cumulative hierarchy of sets function, using Takeuti and Zaring's notation ( R1 ). Starting with the empty set, this function builds up layers of sets where the next layer is the power set of the previous layer (and the union of previous layers when the argument is a limit ordinal). Using the Axiom of Regularity, we can show that any set whatsoever belongs to one of the layers of this hierarchy (see tz9.13 ). Our definition expresses Definition 9.9 of TakeutiZaring p. 76 in a closed form, from which we derive the recursive definition as Theorems r10 , r1suc , and r1lim . Theorem r1val1 shows a recursive definition that works for all values, and Theorems r1val2 and r1val3 show the value expressed in terms of rank. Other notations for this function areR with the argument as a subscript (Equation 3.1 of BellMachover p. 477), _V with a subscript (Definition of Enderton p. 202),M with a subscript (Definition 15.19 of Monk1 p. 113), the capital Greek letter psi (Definition of Mendelson p. 281), and bold-face R (Definition 2.1 of Kunen p. 95). (Contributed by NM, 2-Sep-2003)

Ref Expression
Assertion df-r1 R1 = rec x V 𝒫 x

Detailed syntax breakdown

Step Hyp Ref Expression
0 cr1 class R1
1 vx setvar x
2 cvv class V
3 1 cv setvar x
4 3 cpw class 𝒫 x
5 1 2 4 cmpt class x V 𝒫 x
6 c0 class
7 5 6 crdg class rec x V 𝒫 x
8 0 7 wceq wff R1 = rec x V 𝒫 x