Theorem wl-luk-pm2.21

Description: From a wff and its negation, anything follows. Theorem *2.21 of WhiteheadRussell p. 104. Also called the Duns Scotus law. Copy of pm2.21 with a different proof. (Contributed by Wolf Lammen, 17-Dec-2018) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Assertion	wl-luk-pm2.21	$$⊢\neg \phi \to \left(\phi \to \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		ax-luk3	$$⊢\phi \to \left(\neg \phi \to \psi \right)$$
2	1	wl-luk-com12	$$⊢\neg \phi \to \left(\phi \to \psi \right)$$