how to query foreign keys down more than one level

I have a model like that I would like query down more than one level
(using my nomenclature).

class Library(models.Model)
branch=models.CharField(max_length=100)

class Book(models.Model)
libraryid=models.ForeignKey(Library,related_name="books")

class Chapter(models.Model)
bookid=models.ForeignKey(Book,related_name="chapters")

I can get a library object:

l=Library.objects.filter(branch="Covent Garden")

and then get a query set of all the books in Covent Garden

b=l.books.all()

How do I get a query set of all the chapters (in all the books) in the
Covent Garden library?

then then if I added

class Paragraph(models.Model)
chapterid=models.ForeignKey(Chapter,related_name="paragraphs")

How would I get a query set of all the paragraphs (in all the chapters
in all the books) in the Covent Garden library?

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