how to avoid Cannot redeclare class for 2 diffrent classes with same name

[odziezowka7BB7]

I'm trying to include some functions from phpBB board to my application like a single login. But if i include the common.php it says "Cannot redeclare class user", because my application already has a class user. Is there a way to avoid this ? I tried a little with namespaces, but I never worked with them.So I need a way to include 2 classes with the same name.