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Theorem sbid2v 2456
 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 1840 . 2 𝑥𝜑
21sbid2 2412 1 ([𝑦 / 𝑥][𝑥 / 𝑦]𝜑𝜑)
 Colors of variables: wff setvar class Syntax hints:   ↔ wb 196  [wsb 1877 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1719  ax-4 1734  ax-5 1836  ax-6 1885  ax-7 1932  ax-10 2016  ax-12 2044  ax-13 2245 This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-ex 1702  df-nf 1707  df-sb 1878 This theorem is referenced by:  sbelx  2457  sbco4lem  2464
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