Theorem pm2.01da

Description: Deduction based on reductio ad absurdum. See pm2.01 . (Contributed by Mario Carneiro, 9-Feb-2017)

	Ref	Expression
Hypothesis	pm2.01da.1	$$⊢\left(\phi \wedge \psi \right)\to \neg \psi$$
Assertion	pm2.01da	$$⊢\phi \to \neg \psi$$

Proof

Step	Hyp	Ref	Expression
1		pm2.01da.1	$$⊢\left(\phi \wedge \psi \right)\to \neg \psi$$
2	1	ex	$$⊢\phi \to \left(\psi \to \neg \psi \right)$$
3	2	pm2.01d	$$⊢\phi \to \neg \psi$$