Another example of a ‘two-in-one’ book is Daniel Biebuyck's 'The Mwindo Epic from the Banyanga', a translation of a Bantu prose epic from the Nyanga tribe of eastern Zaire. Read the epic first and enjoy the feats of Mwindo, the epic's hero. Then read the copious footnotes. Much of each page (often more than half the page) is devoted to footnotes which explain things that, since they are well-known to the original narrator's audience，are not explained in performance. Battles which (I assumed) were in the desert are in fact underwater. An opponent who (it seemed) was tall is in fact a giant (there's more, but that would spoil the surprise). Read all the footnotes, then read the epic a second time. Presto! Two books in one!