Feel like a universe destroying book would trigger that no infinite clause but even if it doesn't
then we're back to MAD you can destroy their universe but you cant stop a Pa'anuri that gets into yours.

Except its not quite an even MAD, it takes longer to assemble the book then to fire a long gun, so if they know where you are before you do you just lose. If you do assemble the book you destroy their universe but you cant stop any of them that crosses over, so I guess they just steal your universe?