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Metamath Proof Explorer

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	\|- ( ph -> ps )
	Assertion	notnotd	\|- ( ph -> -. -. ps )

Proof

Step	Hyp	Ref	Expression
1		notnotd.1	\|- ( ph -> ps )
2		notnot	\|- ( ps -> -. -. ps )
3	1 2	syl	\|- ( ph -> -. -. ps )