The Harry Potter series of books is a heptalogy.
A heptalogy, is a compound literary or narrative work that is made up of seven distinct works. The Harry Potter series consists of 7 distinct works. The Chronicles of Narnia consists of 7 distinct works.
∀x (SevenDistinctWorks(x) → Heptalogy(x)) SevenDistinctWorks(harryPotter) SevenDistinctWorks(chroniclesofNarnia)