Theorem fal

Description: The truth value F. is refutable. (Contributed by Anthony Hart, 22-Oct-2010) (Proof shortened by Mel L. O'Cat, 11-Mar-2012)

	Ref	Expression
Assertion	fal	⊢ ¬ ⊥

Proof

Step	Hyp	Ref	Expression
1		tru	⊢ ⊤
2	1	notnoti	⊢ ¬ ¬ ⊤
3		df-fal	⊢ ( ⊥ ↔ ¬ ⊤ )
4	2 3	mtbir	⊢ ¬ ⊥