An immortal woman who is about to go back in time is mailed a book from an unknown address. Inside the book reveals explicit instructions on how not to die while in the past leading up to the present day. The book is written by her future self and mailed to herself by her future self who is now in the present too. Would this be possible? Is it a paradox? Would she be able to write this book and mail it to herself in the present? It would only be written if she had already gone back in time but it also would not have been written if she died in the past having never been given the book to begin with. I am vaguely aware that this is like the age old chicken or the egg conundrum, so I guess I'm just asking a bunch of physics minded people a ridiculous version of that.