Section headings: "to check..." vs. "checking"

Question

I have a technical document which consists of the following sections:

1. Assignment statements
2. Concatenation
3. Data types
4. To check whether key exists
5. To retrieve value
6. To check whether variable or function is True or False
7. Regular expressions
8. Guard statements

What is the best way to name the 4, 5, and 6 sections?

First version:

4. To check whether key exists
5. To retrieve value
6. To check whether variable or function is True or False

or maybe

4. Checking whether key exists
5. Retrieving value
6. Checking whether variable or function is True or False

or maybe

4. Check whether key exists
5. Retrieving value
6. Check whether variable or function is True or False

English is not my native language.

Answer 1

Typically, the title of a procedural topic uses the gerund of the verb. For example, "Checking..." However, this can vary by organization and depends on the style guide or conventions your organization has established.

Answer 2

The accepted answer is correct of course, but I want to add that you can also use the "How to" construction:

4. How to check whether a key exists
5. How to retrieve a value
6. How to check whether variable or function is True or False

This phrasing is also used in procedural topics, though less common.

Versions 1 and 3 are usually used in procedures themselves:

To check whether a key exists:
1. Open the registry editor.
2. ...