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Theorem sbid2v 1869
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 1416 . 2 (φxφ)
21sbid2h 1726 1 ([y / x][x / y]φφ)
Colors of variables: wff set class
Syntax hints:  wb 98  [wsb 1642
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 1333  ax-gen 1335  ax-ie1 1379  ax-ie2 1380  ax-8 1392  ax-11 1394  ax-4 1397  ax-17 1416  ax-i9 1420  ax-ial 1424
This theorem depends on definitions:  df-bi 110  df-sb 1643
This theorem is referenced by:  bdph  9285
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