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Theorem xchnxbir 300
Description: Replacement of a subexpression by an equivalent one. (Contributed by Wolf Lammen, 27-Sep-2014.)
Hypotheses
Ref Expression
xchnxbir.1 φψ)
xchnxbir.2 (χφ)
Assertion
Ref Expression
xchnxbir χψ)

Proof of Theorem xchnxbir
StepHypRef Expression
1 xchnxbir.1 . 2 φψ)
2 xchnxbir.2 . . 3 (χφ)
32bicomi 193 . 2 (φχ)
41, 3xchnxbi 299 1 χψ)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 176
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 177
This theorem is referenced by:  3ioran  950  nsspssun  3488  undif3  3515
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