Theorem neutru

Description: There does not exist exactly one set such that T. is true. (Contributed by Anthony Hart, 13-Sep-2011)

	Ref	Expression
Assertion	neutru	$$⊢\neg \exists !x\top$$

Proof

Step	Hyp	Ref	Expression
1		nexntru	$$⊢\neg \exists x\neg \top$$
2		eunex	$$⊢\exists !x\top \to \exists x\neg \top$$
3	1 2	mto	$$⊢\neg \exists !x\top$$