Definition df-nfc 2529

Description: Define the not-free predicate for classes. This is read " x is not free in A". Not-free means that the value of x cannot affect the value of A, e.g., any occurrence of x in A is effectively bound by a "for all" or something that expands to one (such as "there exists"). It is defined in terms of the not-free predicate df-nf 1551 for wffs; see that definition for more information. (Contributed by Mario Carneiro, 11-Aug-2016.)

Assertion

Ref	Expression
df-nfc	|- ( F/_ x A <-> A. y F/ x y e. A )

Distinct variable groups:   x, y   y, A

Allowed substitution hint:   A( x)

Detailed syntax breakdown of Definition df-nfc

Step	Hyp	Ref	Expression
1		vx	. . 3 set x
2		cA	. . 3 class A
3	1, 2	wnfc 2527	. 2 wff F/_ x A
4		vy	. . . . . 6 set y
5	4	cv 1648	. . . . 5 class y
6	5, 2	wcel 1721	. . . 4 wff y e. A
7	6, 1	wnf 1550	. . 3 wff F/ x y e. A
8	7, 4	wal 1546	. 2 wff A. y F/ x y e. A
9	3, 8	wb 177	1 wff ( F/_ x A <-> A. y F/ x y e. A )

This definition is referenced by:  nfci  2530  nfcr  2532  nfcd  2535  nfceqi  2536  nfceqdf  2539  nfnfc1  2543  nfnfc  2546  drnfc1  2556  drnfc2  2557  dfnfc2  3993  nfnid  4353