But since almost every heresy (that has sprung up) through the arithmetical art has discovered measures of hebdomads and certain projections of Æons, each rending the art differently, while whatever variation prevailed was in the names merely; and (since) Pythagoras became the instructor of these, first introducing numbers of this sort among the Greeks from Egypt, it seems expedient not to omit even this, but, after we have given a compendious elucidation, to approach the demonstration of those things that we propose to investigate.