That's interesting, many countries have laws(or customs) to submit everything published in a form of a book to the national library. I know here in Poland this

That's interesting, many countries have laws(or customs) to submit everything published in a form of a book to the national library. I know here in Poland this is done too, because my partner was having her book published by a small publisher and "providing a copy of the book to the national library" was one of the publisher's responsibilities. I have no idea if it's a law or just a custom.