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Metamath Proof Explorer

Theorem pm2.21ddALT

Description: Alternate proof of pm2.21dd . (Contributed by Mario Carneiro, 9-Feb-2017) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypotheses	pm2.21ddALT.1	$⊢ φ \to ψ$
	pm2.21ddALT.2	$⊢ φ \to \neg ψ$
Assertion	pm2.21ddALT	$⊢ φ \to χ$

Proof

Step	Hyp	Ref	Expression
1		pm2.21ddALT.1	$⊢ φ \to ψ$
2		pm2.21ddALT.2	$⊢ φ \to \neg ψ$
3	2	pm2.21d	$⊢ φ \to (ψ \to χ)$
4	1 3	mpd	$⊢ φ \to χ$