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Definition df-nfc 2581
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 1668 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
StepHypRef Expression
1 vx . . 3  setvar  x
2 cA . . 3  class  A
31, 2wnfc 2579 . 2  wff  F/_ x A
4 vy . . . . . 6  setvar  y
54cv 1443 . . . . 5  class  y
65, 2wcel 1887 . . . 4  wff  y  e.  A
76, 1wnf 1667 . . 3  wff  F/ x  y  e.  A
87, 4wal 1442 . 2  wff  A. y F/ x  y  e.  A
93, 8wb 188 1  wff  ( F/_ x A  <->  A. y F/ x  y  e.  A )
Colors of variables: wff setvar class
This definition is referenced by:  nfci  2582  nfcr  2584  nfcd  2587  nfceqdf  2588  nfnfc1  2595  nfnfc  2601  nfnfcALT  2602  drnfc1  2609  drnfc2  2610  dfnfc2  4216  nfnid  4629  bj-nfnfc  31462  bj-nfcf  31527
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