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Theorem falnorfalOLD 1596
Description: Obsolete version of falnorfal 1595 as of 17-Dec-2023. (Contributed by Remi, 25-Oct-2023.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
falnorfalOLD ((⊥ ⊥) ↔ ⊤)

Proof of Theorem falnorfalOLD
StepHypRef Expression
1 df-nor 1525 . 2 ((⊥ ⊥) ↔ ¬ (⊥ ∨ ⊥))
2 notfal 1569 . . . . 5 (¬ ⊥ ↔ ⊤)
32bicomi 223 . . . 4 (⊤ ↔ ¬ ⊥)
4 falorfal 1581 . . . . 5 ((⊥ ∨ ⊥) ↔ ⊥)
54bicomi 223 . . . 4 (⊥ ↔ (⊥ ∨ ⊥))
63, 5xchbinx 333 . . 3 (⊤ ↔ ¬ (⊥ ∨ ⊥))
76bicomi 223 . 2 (¬ (⊥ ∨ ⊥) ↔ ⊤)
81, 7bitri 274 1 ((⊥ ⊥) ↔ ⊤)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 205  wo 843   wnor 1524  wtru 1542  wfal 1553
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 206  df-or 844  df-nor 1525  df-tru 1544  df-fal 1554
This theorem is referenced by: (None)
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