Altaïr nodded. "Books, yes," he agreed, "but if they have been already written, they cannot be written on again."

But then...

Then he considered. How were these books made? He had seen some copied where signatures at the end were empty, where some pages were blank. Would it be horrid to go and find these blank pages and use them?

"But there is a possibility. I'll have to go and look at this library. See what I can find."