> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/u/union.md).

# union

## union

The set of elements that are members of\*\*\*\* at least one of two or more sets.

#### Notes

* In set theory, the union of a collection of sets is the set of all elements in the collection.
* In SNOMED CT, the *union* of two or more \_subsets \_of concepts consists of all concepts that are members of at least one of those subsets.

#### Examples

* The following expression constraint language defines the set of concepts in the union of subtypes of [7569003 | Finger|](http://snomed.info/id/7569003) and subtypes of [76505004 | Thumb structure|](http://snomed.info/id/76505004) . The "OR" instruction indicates a union between the sets defined by constraints on either side of that instruction.

<< [7569003 |Finger|](http://snomed.info/id/7569003)\
OR << [76505004 |Thumb structure|](http://snomed.info/id/76505004)

## Related Links

* Wikipedia
  * [Union (set theory)](https://en.wikipedia.org/wiki/Union_\(set_theory\))

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