Theorem vexOLD

Description: Obsolete version of vex as of 28-Aug-2023. All setvar variables are sets (see isset ). Theorem 6.8 of Quine p. 43. (Contributed by NM, 26-May-1993) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Assertion	vexOLD	$$⊢x\in \mathrm{V}$$

Proof

Step	Hyp	Ref	Expression
1		equid	$$⊢x=x$$
2		df-v	$$⊢\mathrm{V}=\left\{x|x=x\right\}$$
3	2	abeq2i	$$⊢x\in \mathrm{V}\leftrightarrow x=x$$
4	1 3	mpbir	$$⊢x\in \mathrm{V}$$