Theorem neq0OLD

Description: Obsolete version of neq0 as of 28-Jun-2024. (Contributed by NM, 21-Jun-1993) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	neq0OLD	$$⊢\neg A=\varnothing \leftrightarrow \exists xx\in A$$

Proof

Step	Hyp	Ref	Expression
1		nfcv	$$⊢\underset{\_}{Ⅎ}xA$$
2	1	neq0f	$$⊢\neg A=\varnothing \leftrightarrow \exists xx\in A$$