^Michael Wright (January 2, 2000). "The Marcel wave". The Times. "The pressure to read Proust is felt in different ways. Sir Richard Eyre ... confesses that he was shamed into reading the mighty heptalogy by Alan Bennett."
Alan Farrell (2007). High Cheekbones, Pouty Lips, Tight Jeans. s. 227. "...while Lewis confected a heptalogy ... about the fictitious and snow-shrouded land of Narnia...."
Michael Ward. Planet Narnia. The Seven Heavens in the Imagination of C.S. Lewis. s. 13. "Charles Wrong ... reports Lewis as adding, "I had to write three volumes, of course, or seven, or nine. Those are the magic numbers.""
^School Library Association of New Zealand Aotearoa Newsletter 11, December 2003, p. 9. ISSN 1175-5555. .