Definition:Set Union/Finite Union

Definition
In the general definition of union, if the indexing set $I$ or the set of sets $\mathbb S$ is finite, then the term finite union is used.

The union of $X_1, X_2, \ldots, X_n$ is denoted:
 * $X_1 \cup X_2 \cup \cdots \cup X_n$
 * $\displaystyle \bigcup_{k \mathop = 1}^n X_k$
 * $\displaystyle \bigcup_{1 \mathop \le k \mathop \le n} X_k$