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Theorem nfsb4 2131
Description: A variable not free remains so after substitution with a distinct variable. (Contributed by NM, 14-May-1993.) (Revised by Mario Carneiro, 4-Oct-2016.)
Hypothesis
Ref Expression
nfsb4.1
Assertion
Ref Expression
nfsb4

Proof of Theorem nfsb4
StepHypRef Expression
1 nfsb4t 2130 . 2
2 nfsb4.1 . 2
31, 2mpg 1620 1
Colors of variables: wff setvar class
Syntax hints:  -.wn 3  ->wi 4  A.wal 1393  F/wnf 1616  [wsb 1739
This theorem is referenced by:  sbco2  2158  nfsb  2184
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1618  ax-4 1631  ax-5 1704  ax-6 1747  ax-7 1790  ax-10 1837  ax-11 1842  ax-12 1854  ax-13 1999
This theorem depends on definitions:  df-bi 185  df-an 371  df-ex 1613  df-nf 1617  df-sb 1740
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