Question

Hello,
Sorry for opening a new thread; for some reason I’m not able to reply in one of the existing ones.
Sorry it wasn’t clear: I meant that I found a book in a public place, and it says on it that it belongs to a library. I’m not connected to the questioner and don’t know him. The question was what I need to do now with the book.
Is there an obligation on me, under the law of returning a lost item, to return it to the library? Or to the borrower? Or perhaps to neither of them, since the library has already collected the money for it?