I think this is exactly why
exists. As Fou-Lu suggested it's a good idea to keep a sense of your file interrelations, and kind-of not go nuts on the duplicate requests. However, if you've got yourself into a corner — or just don't know for that matter — then using
should definately keep you out of any real trouble with multi-inclusion.
One important pitfall to note, consider this:
This will execute file.php twice, since a non
inclusion will not even check if a
has occured previously. If you want to be safe, use
with all inclusions!