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Theorem sbid2v 2123
Description: An identity law for substitution. Used in proof of Theorem 9.7 of [Megill] p. 449 (p. 16 of the preprint). (Contributed by NM, 5-Aug-1993.)
Assertion
Ref Expression
sbid2v ([y / x][x / y]φφ)
Distinct variable group:   φ,x
Allowed substitution hint:   φ(y)

Proof of Theorem sbid2v
StepHypRef Expression
1 nfv 1619 . 2 xφ
21sbid2 2084 1 ([y / x][x / y]φφ)
Colors of variables: wff setvar class
Syntax hints:  wb 176  [wsb 1648
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  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925
This theorem depends on definitions:  df-bi 177  df-an 360  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649
This theorem is referenced by:  sbelx  2124
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