Douglas M. Parrott writes (The Nag Hammadi Library in English, p. 322):
Evidence that Disc. 8-9 was composed in Egypt is found in references to the city of Diospolis, as well as to hieroglyphic characters and gods with animal faces - all found in the section beginning 61,18. The designation of the mystagogue sa Hermes and Trismegistus also suggests Egypt. A second-century C.E. date for the composition is possible, because of affinities with the thought of the Middle Platonist Albinus.
The reference to "eighth" and "ninth" is to the spheres of the heavens that surround the earth.
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