Theorem nexr

Description: Inference associated with the contrapositive of 19.8a . (Contributed by Jeff Hankins, 26-Jul-2009)

	Ref	Expression
Hypothesis	nexr.1	$$⊢\neg \exists x\phi$$
Assertion	nexr	$$⊢\neg \phi$$

Proof

Step	Hyp	Ref	Expression
1		nexr.1	$$⊢\neg \exists x\phi$$
2		19.8a	$$⊢\phi \to \exists x\phi$$
3	1 2	mto	$$⊢\neg \phi$$