Metamath Proof Explorer


Theorem vuniex

Description: The union of a setvar is a set. (Contributed by BJ, 3-May-2021) (Revised by BJ, 6-Apr-2024)

Ref Expression
Assertion vuniex
|- U. x e. _V

Proof

Step Hyp Ref Expression
1 uniex2
 |-  E. y y = U. x
2 1 issetri
 |-  U. x e. _V