Killa_robot's codex won't work in conjunction with another item.
For example, if you use item 1, then use the codex, the codex will ALWAYS remember the last page you was on, and that last page is whatever page item 1 brings you to.
That being say, once you press the previous page on page 1, it will bring you back to the codex.
Pressing the codex will bring you back to what page item 1 brings you to.
Then it will go in an infinite loop.
I suggest you find anothey way to do this.