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Theorem frege68a 42246
Description: Combination of applying a definition and applying it to a specific instance. Proposition 68 of [Frege1879] p. 54. (Contributed by RP, 17-Apr-2020.) (Proof modification is discouraged.)
Assertion
Ref Expression
frege68a (((𝜓𝜒) ↔ 𝜃) → (𝜃 → if-(𝜑, 𝜓, 𝜒)))

Proof of Theorem frege68a
StepHypRef Expression
1 frege57aid 42232 . 2 (((𝜓𝜒) ↔ 𝜃) → (𝜃 → (𝜓𝜒)))
2 frege67a 42245 . 2 ((((𝜓𝜒) ↔ 𝜃) → (𝜃 → (𝜓𝜒))) → (((𝜓𝜒) ↔ 𝜃) → (𝜃 → if-(𝜑, 𝜓, 𝜒))))
31, 2ax-mp 5 1 (((𝜓𝜒) ↔ 𝜃) → (𝜃 → if-(𝜑, 𝜓, 𝜒)))
Colors of variables: wff setvar class
Syntax hints:  wi 4  wb 205  wa 397  if-wif 1062
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-frege1 42150  ax-frege2 42151  ax-frege8 42169  ax-frege52a 42217  ax-frege58a 42235
This theorem depends on definitions:  df-bi 206  df-an 398  df-or 847  df-ifp 1063  df-tru 1545  df-fal 1555
This theorem is referenced by: (None)
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