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Metamath Proof Explorer

Theorem nbn3

Description: Transfer falsehood via equivalence. (Contributed by NM, 11-Sep-2006)

		Ref	Expression
	Hypothesis	nbn3.1	$⊢ φ$
	Assertion	nbn3	$⊢ \neg ψ \leftrightarrow (ψ \leftrightarrow \neg φ)$

Step	Hyp	Ref	Expression
1		nbn3.1	$⊢ φ$
2	1	notnoti	$⊢ \neg \neg φ$
3	2	nbn	$⊢ \neg ψ \leftrightarrow (ψ \leftrightarrow \neg φ)$