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Theorem nornotOLD 1526
Description: Obsolete version of nornot 1525 as of 8-Dec-2023. (Contributed by Remi, 25-Oct-2023.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
nornotOLD 𝜑 ↔ (𝜑 𝜑))

Proof of Theorem nornotOLD
StepHypRef Expression
1 pm4.56 986 . 2 ((¬ 𝜑 ∧ ¬ 𝜑) ↔ ¬ (𝜑𝜑))
2 pm4.24 567 . 2 𝜑 ↔ (¬ 𝜑 ∧ ¬ 𝜑))
3 df-nor 1522 . 2 ((𝜑 𝜑) ↔ ¬ (𝜑𝜑))
41, 2, 33bitr4i 306 1 𝜑 ↔ (𝜑 𝜑))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 209  wa 399  wo 844   wnor 1521
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 210  df-an 400  df-or 845  df-nor 1522
This theorem is referenced by: (None)
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