Theorem efald

Description: Deduction based on reductio ad absurdum. (Contributed by Mario Carneiro, 9-Feb-2017)

	Ref	Expression
Hypothesis	efald.1	$$⊢\left(\phi \wedge \neg \psi \right)\to \perp$$
Assertion	efald	$$⊢\phi \to \psi$$

Proof

Step	Hyp	Ref	Expression
1		efald.1	$$⊢\left(\phi \wedge \neg \psi \right)\to \perp$$
2	1	inegd	$$⊢\phi \to \neg \neg \psi$$
3	2	notnotrd	$$⊢\phi \to \psi$$