require_once()
PHP also gives us require_once(), another structure to intelligently include files.

The PHP documentation for require_once() says:

The require_once statement is identical to require except PHP will check if the file has already been included, and if so, not include (require) it again.
Exercises
Open the file address_book.php for editing. Commit and push after each change.

Update your file to require_once(), not include(), your class.