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Theorem biorfiOLD 422
Description: Obsolete proof of biorfi 421 as of 16-Jul-2021. (Contributed by NM, 23-Mar-1995.) (Proof modification is discouraged.) (New usage is discouraged.)
Hypothesis
Ref Expression
biorfi.1 ¬ 𝜑
Assertion
Ref Expression
biorfiOLD (𝜓 ↔ (𝜓𝜑))

Proof of Theorem biorfiOLD
StepHypRef Expression
1 biorfi.1 . 2 ¬ 𝜑
2 orc 399 . . 3 (𝜓 → (𝜓𝜑))
3 orel2 397 . . 3 𝜑 → ((𝜓𝜑) → 𝜓))
42, 3impbid2 216 . 2 𝜑 → (𝜓 ↔ (𝜓𝜑)))
51, 4ax-mp 5 1 (𝜓 ↔ (𝜓𝜑))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 196  wo 382
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 197  df-or 384
This theorem is referenced by: (None)
  Copyright terms: Public domain W3C validator