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	⊢ ( ( ¬ 𝜑 → ¬ 𝜓 ) → ( 𝜓 → 𝜑 ) )

Proof

Step	Hyp	Ref	Expression
1		ax-3	⊢ ( ( ¬ 𝜑 → ¬ 𝜓 ) → ( 𝜓 → 𝜑 ) )