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Theorem nfnf 1857
Description: If  x is not free in  ph, it is not free in  F/ y ph. (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 30-Dec-2017.)
Hypothesis
Ref Expression
nfal.1  |-  F/ x ph
Assertion
Ref Expression
nfnf  |-  F/ x F/ y ph

Proof of Theorem nfnf
StepHypRef Expression
1 df-nf 1551 . 2  |-  ( F/ y ph  <->  A. y
( ph  ->  A. y ph ) )
2 nfal.1 . . . 4  |-  F/ x ph
32nfal 1854 . . . 4  |-  F/ x A. y ph
42, 3nfim 1822 . . 3  |-  F/ x
( ph  ->  A. y ph )
54nfal 1854 . 2  |-  F/ x A. y ( ph  ->  A. y ph )
61, 5nfxfr 1576 1  |-  F/ x F/ y ph
Colors of variables: wff set class
Syntax hints:    -> wi 4   A.wal 1546   F/wnf 1550
This theorem is referenced by:  nfnfc  2530
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1552  ax-5 1563  ax-17 1623  ax-9 1661  ax-8 1682  ax-6 1736  ax-7 1741  ax-11 1753
This theorem depends on definitions:  df-bi 178  df-ex 1548  df-nf 1551
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