> 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/c/complement.md).

# complement

The set of elements that are **not** in a specified set.

### Notes

* In set theory, the *complement* of set \*\* *A*\*\* refers to all elements not in set \*\* *A*\*\*.
* In SNOMED CT, the *complement* of a \_subset \_of concepts consists of all concepts that are not in that subset.

### Example

* The following expression constraint language defines the set of concepts that are subtypes of [442083009 | Anatomical or acquired body structure|](http://snomed.info/id/442083009) that are also part of the *complement* of the [723264001 | Lateralizable body structure reference set|](http://snomed.info/id/723264001) . The "MINUS" instruction excludes members of the reference set, so only concepts that are part of the *complement* of that set are included.

< [442083009 |Anatomical or acquired body structure|](http://snomed.info/id/442083009)\
MINUS ^ [723264001 |Lateralizable body structure reference set|](http://snomed.info/id/723264001)

Related Links

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

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