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Metamath Proof Explorer

Theorem pm2.521

Description: Theorem *2.521 of WhiteheadRussell p. 107. Instance of pm2.521g and of pm2.521g2 . (Contributed by NM, 3-Jan-2005)

		Ref	Expression
	Assertion	pm2.521	$⊢ \neg (φ \to ψ) \to (ψ \to φ)$

Step	Hyp	Ref	Expression
1		pm2.521g	$⊢ \neg (φ \to ψ) \to (ψ \to φ)$