Theorem bj-con4iALT 31717

Description: Alternate proof of con4i 112. Probably the original proof. (Contributed by BJ, 29-Mar-2020.) (New usage is discouraged.) (Proof modification is discouraged.)

Hypothesis

Ref	Expression
bj-con4iALT.1	⊢ (¬ 𝜑 → ¬ 𝜓)

Assertion

Ref	Expression
bj-con4iALT	⊢ (𝜓 → 𝜑)

Proof of Theorem bj-con4iALT

Step	Hyp	Ref	Expression
1		bj-con4iALT.1	. 2 ⊢ (¬ 𝜑 → ¬ 𝜓)
2		con4 111	. 2 ⊢ ((¬ 𝜑 → ¬ 𝜓) → (𝜓 → 𝜑))
3	1, 2	ax-mp 5	1 ⊢ (𝜓 → 𝜑)

Syntax hints:  ¬ wn 3   → wi 4

This theorem was proved from axioms:  ax-mp 5  ax-3 8

This theorem is referenced by: (None)