Theorem notnotd

Description: Deduction associated with notnot and notnoti . (Contributed by Jarvin Udandy, 2-Sep-2016) Avoid biconditional. (Revised by Wolf Lammen, 27-Mar-2021)

	Ref	Expression
Hypothesis	notnotd.1	⊢ ( 𝜑 → 𝜓 )
Assertion	notnotd	⊢ ( 𝜑 → ¬ ¬ 𝜓 )

Proof

Step	Hyp	Ref	Expression
1		notnotd.1	⊢ ( 𝜑 → 𝜓 )
2		notnot	⊢ ( 𝜓 → ¬ ¬ 𝜓 )
3	1 2	syl	⊢ ( 𝜑 → ¬ ¬ 𝜓 )