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