# Set-specific operations

The Kotlin collections package contains extension functions for popular operations on sets: finding intersections, merging, or subtracting collections from each other.

To merge two collections into one, use the `union()`

function. It can be used in the infix form `a union b`

. Note that for ordered collections the order of the operands is important: in the resulting collection, the elements of the first operand go before the elements of the second.

To find an intersection between two collections (elements present in both of them), use `intersect()`

. To find collection elements not present in another collection, use `subtract()`

. Both these functions can be called in the infix form as well, for example, `a intersect b`

.

Note that set operations are supported by `List`

as well. However, the result of set operations on lists is still a `Set`

, so all the duplicate elements are removed.