Question for those who have read "The Dogs of Babel"?

Towards the end of the book, when Paul finally realized that Lexy must have killed herself, he looks at all the book title in the order in which Lexy arranged them before she died. I know there's some sort of clue in it tht has something to so with the story of Tam Lin, but I can't figure out wht it is. Can anyone explain it to me?