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Theorem sbid2v 1850
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 ax-17 1396 . 2 (φxφ)
21sbid2h 1707 1 ([y / x][x / y]φφ)
Colors of variables: wff set class
Syntax hints:  wb 98  [wsb 1623
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-5 1312  ax-gen 1314  ax-ie1 1359  ax-ie2 1360  ax-8 1372  ax-11 1374  ax-4 1377  ax-17 1396  ax-i9 1400  ax-ial 1405
This theorem depends on definitions:  df-bi 110  df-sb 1624
This theorem is referenced by:  bdph  7269
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