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Metamath Proof Explorer

Theorem con4

Description: Alias for ax-3 to be used instead of it for labeling consistency. Its associated inference is con4i and its associated deduction is con4d . (Contributed by BJ, 24-Dec-2020)

		Ref	Expression
	Assertion	con4	$⊢ (\neg φ \to \neg ψ) \to (ψ \to φ)$

Proof

Step	Hyp	Ref	Expression
1		ax-3	$⊢ (\neg φ \to \neg ψ) \to (ψ \to φ)$