# Exercise 9: Cross-referencing content

In this exercise, you will learn how to create references to other parts of your book, such as chapters, sections, equations, tables, and figures.

::::::{topic} Exercise objective
Can you create internal references to other sections, equations, tables, and figures?
::::::

```{tip}
Referencing elements properly ensures that readers can navigate your book more easily. More details can be found in the [JupyterBook documentation](https://jupyterbook.org/en/stable/content/references.html).
```

## 1. Referencing a Chapter or Section

To create a reference to another chapter or section, use the following syntax:

```md
[Text to display](path/to/file.md)
```

For example, if you want to link to Exercise 7, you can write:

```md
[Go to Exercise 7](../exercises/007.md)
```

Alternatively, you can use `{ref}` to reference a section with a target header.

First, define the section you want to reference by assigning it an identifier:

```md
(exercise_1)=
# Exercise 1: First file edit

Let's start with the most basic edit: add some text to a file and see that the website is updated...
```

Then, you can reference this section in three ways:

- Using the standard title text:
  ```md
  My favourite exercise was {ref}`exercise_1`.
  ```
  This will display: *My favourite exercise was Exercise 1: First file edit.*

- Specifying a custom title text:
  ```md
  My favourite exercise was {ref}`the first one <exercise_1>`.
  ```
  This will display: *My favourite exercise was the first one.*

- Using Markdown syntax:
  ```md
  My favourite exercise was [this one](exercise_1).
  ```
  This will display: *My favourite exercise was this one.*

## 2. Referencing an Equation

To reference an equation, you need to define a label using `{eq}` and refer to it elsewhere in your text:

```md
```{math}
:label: eq-example
E = mc^2
```
```

You can then reference this equation using:

```md
Equation {eq}`eq-example`
```

## 3. Referencing a Table

To reference a table, assign a label when defining it:

```md
```{table} Example Table
:label: tab-example
| Column 1 | Column 2 |
|----------|----------|
| A        | B        |
```
```

And refer to it using:

```md
Table {numref}`tab-example`
```

## 4. Referencing a Figure

To reference a figure, label it when inserting it:

```md
```{figure} figures/example.png
---
width: 80%
align: center
name: fig-example
---
Example figure.
```
```

And refer to it using:

```md
Figure {numref}`fig-example`
```

## 5. Commit Your Changes

1. Once you have added your references, commit your changes to the repository.
2. Click the green `Commit changes` button.
3. Add a commit message.
4. View your changes using the `Actions` tab and check if they appear correctly.

```{admonition} Check your understanding
:class: note

Before moving on to the next exercise, make sure you understand the following:
- How do you reference another chapter or section?
- How do you create a reference to an equation?
- How can you refer to a table or a figure in your book?