Theorem nornotOLD

Description: Obsolete version of nornot as of 8-Dec-2023. (Contributed by Remi, 25-Oct-2023) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	nornotOLD	⊢ ( ¬ 𝜑 ↔ ( 𝜑 ⊽ 𝜑 ) )

Proof

Step	Hyp	Ref	Expression
1		pm4.56	⊢ ( ( ¬ 𝜑 ∧ ¬ 𝜑 ) ↔ ¬ ( 𝜑 ∨ 𝜑 ) )
2		pm4.24	⊢ ( ¬ 𝜑 ↔ ( ¬ 𝜑 ∧ ¬ 𝜑 ) )
3		df-nor	⊢ ( ( 𝜑 ⊽ 𝜑 ) ↔ ¬ ( 𝜑 ∨ 𝜑 ) )
4	1 2 3	3bitr4i	⊢ ( ¬ 𝜑 ↔ ( 𝜑 ⊽ 𝜑 ) )