Theorem atbiffatnnbalt

Description: If a implies b, then a implies not not b. (Contributed by Jarvin Udandy, 29-Aug-2016)

	Ref	Expression
Assertion	atbiffatnnbalt	$$⊢\left(\phi \to \psi \right)\to \left(\phi \to \neg \neg \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		atbiffatnnb	$$⊢\left(\phi \to \psi \right)\to \left(\phi \to \neg \neg \psi \right)$$