Theorem wl-luk-pm2.18d

Description: Deduction based on reductio ad absurdum. Copy of pm2.18d with a different proof. (Contributed by Wolf Lammen, 17-Dec-2018) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Hypothesis	wl-luk-pm2.18d.1	$$⊢\phi \to \left(\neg \psi \to \psi \right)$$
Assertion	wl-luk-pm2.18d	$$⊢\phi \to \psi$$

Proof

Step	Hyp	Ref	Expression
1		wl-luk-pm2.18d.1	$$⊢\phi \to \left(\neg \psi \to \psi \right)$$
2		ax-luk2	$$⊢\left(\neg \psi \to \psi \right)\to \psi$$
3	1 2	wl-luk-syl	$$⊢\phi \to \psi$$