Theorem trunorfalOLD

Description: Obsolete version of trunorfal as of 17-Dec-2023. (Contributed by Remi, 25-Oct-2023) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	trunorfalOLD	⊢ ( ( ⊤ ⊽ ⊥ ) ↔ ⊥ )

Proof

Step	Hyp	Ref	Expression
1		df-nor	⊢ ( ( ⊤ ⊽ ⊥ ) ↔ ¬ ( ⊤ ∨ ⊥ ) )
2		tru	⊢ ⊤
3	2	orci	⊢ ( ⊤ ∨ ⊥ )
4	3	notnoti	⊢ ¬ ¬ ( ⊤ ∨ ⊥ )
5	4	bifal	⊢ ( ¬ ( ⊤ ∨ ⊥ ) ↔ ⊥ )
6	1 5	bitri	⊢ ( ( ⊤ ⊽ ⊥ ) ↔ ⊥ )