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Metamath Proof Explorer

Theorem pm2.621

Description: Theorem *2.621 of WhiteheadRussell p. 107. (Contributed by NM, 3-Jan-2005)

		Ref	Expression
	Assertion	pm2.621	$⊢ (φ \to ψ) \to ((φ \lor ψ) \to ψ)$

Step	Hyp	Ref	Expression
1		id	$⊢ (φ \to ψ) \to (φ \to ψ)$
2		idd	$⊢ (φ \to ψ) \to (ψ \to ψ)$
3	1 2	jaod	$⊢ (φ \to ψ) \to ((φ \lor ψ) \to ψ)$