> For the complete documentation index, see [llms.txt](https://php-fhir-tools.ardenexal.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://php-fhir-tools.ardenexal.net/fhirpath/functions/existence.md).

# Existence & Collection

Functions that test for the presence, count, and ordering relationships of items in a collection. Most return a single Boolean.

| Function             | Description                                                                                            | Example                                    |
| -------------------- | ------------------------------------------------------------------------------------------------------ | ------------------------------------------ |
| `empty()`            | True when the input collection has no items.                                                           | `Patient.name.empty()`                     |
| `exists([criteria])` | True when the collection is non-empty; with an optional filter expression, true when any item matches. | `Patient.telecom.exists(system = 'phone')` |
| `all(criteria)`      | True when every item matches the given expression (true for an empty input).                           | `Patient.name.all(use = 'official')`       |
| `count()`            | Returns the number of items as an Integer.                                                             | `Patient.name.count()`                     |
| `allTrue()`          | True when every Boolean item is true.                                                                  | `Patient.active.allTrue()`                 |
| `anyTrue()`          | True when at least one Boolean item is true.                                                           | `(true \| false).anyTrue()`                |
| `allFalse()`         | True when every Boolean item is false.                                                                 | `(false \| false).allFalse()`              |
| `anyFalse()`         | True when at least one Boolean item is false.                                                          | `(true \| false).anyFalse()`               |
| `subsetOf(other)`    | True when every item in the input also exists in `other`.                                              | `name.subsetOf(%context.name)`             |
| `supersetOf(other)`  | True when every item in `other` also exists in the input.                                              | `name.supersetOf(%context.name)`           |
| `isDistinct()`       | True when the collection contains no duplicate items.                                                  | `Patient.name.given.isDistinct()`          |
| `not()`              | Logical negation of a single Boolean input (function form of `!`).                                     | `Patient.active.not()`                     |

{% hint style="info" %}
The tree-traversal helper `repeat()` is documented under [Tree Navigation & Utility](/fhirpath/functions/navigation.md).
{% endhint %}


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