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Theorem nfequid 1678
Description: Bound-variable hypothesis builder for x = x. This theorem tells us that any variable, including x, is effectively not free in x = x, even though x is technically free according to the traditional definition of free variable. (Contributed by NM, 13-Jan-2011.) (Revised by NM, 21-Aug-2017.)
Ref Expression
nfequid y x = x

Proof of Theorem nfequid
StepHypRef Expression
1 equid 1676 . 2 x = x
21nfth 1553 1 y x = x
Colors of variables: wff setvar class
Syntax hints:  wnf 1544
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675
This theorem depends on definitions:  df-bi 177  df-ex 1542  df-nf 1545
This theorem is referenced by: (None)
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