## Union

### Set

context | $X,Y$ … set |

definiendum | $ x\in X \cup Y $ |

postulate | $ x\in X\lor x\in Y $ |

### Discussion

The 2-ary set construction $ X \cup Y $ is commutative and idempotent.

Notice that $ X \cup \emptyset = X$.

The union and intersection are associative and distributive with respect to another.

#### Reference

Wikipedia: Union