# Introduction

| [Calculations](https://help.clause9.com/special-functions/calculations)             | [Concepts](https://help.clause9.com/special-functions/concepts)             | [Conditions](https://help.clause9.com/special-functions/conditions)                 |
| ----------------------------------------------------------------------------------- | --------------------------------------------------------------------------- | ----------------------------------------------------------------------------------- |
| [Conjugations](https://help.clause9.com/special-functions/conjugations)             | [Content Control](https://help.clause9.com/special-functions/special-items) | [Datafields](https://help.clause9.com/special-functions/datafields)                 |
| [Dates & durations](https://help.clause9.com/special-functions/dates-and-durations) | [Languages](https://help.clause9.com/special-functions/languages)           | [Lists](https://help.clause9.com/special-functions/lists)                           |
| [Numbers](https://help.clause9.com/special-functions/numbers)                       | [References](https://help.clause9.com/special-functions/references)         | [Repeating (looping)](https://help.clause9.com/special-functions/repeating-looping) |
| [Special items](https://help.clause9.com/special-functions/special-items-1)         | [Text Structure](https://help.clause9.com/special-functions/text-structure) | [Text modification](https://help.clause9.com/special-functions/text-modification)   |
| [Users](https://help.clause9.com/special-functions/user)                            | [Q\&A](https://help.clause9.com/special-functions/q-and-a)                  |                                                                                     |

{% embed url="<https://vimeo.com/428497901>" %}

## Usage tips

* Don’t forget that each of the special functions below can be combined with other special functions, through AND / OR.
* Every special function that returns true/false can be “inverted” by wrapping it in a NOT. For example, not(`@assigned(#concept^datafield))` will return `true` if that datafield is *not* assigned a value.
* When you are typing in the name of a function in the editor, you can get a list of matching functions by pressing Control + Spacebar after you have inserted the @-symbol and at least a few letters:

<figure><img src="/files/NhyNt13W7KI22KedS31f" alt="" width="313"><figcaption></figcaption></figure>

* When you want to get a summary of the function’s purpose and its arguments, you can press the same shortcut Control + Spacebar when your cursor is between the parentheses of that function:

<figure><img src="/files/N47EbYvY3JgB3yGbnUqa" alt="" width="563"><figcaption></figcaption></figure>


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