While in synagogue on Yom Kippur a few days ago, I noticed (for the first time) that the "song of the day" in the Machzor (prayer book just for Yom Kippur) only

While in synagogue on Yom Kippur a few days ago, I noticed (for the first time) that the "song of the day" in the Machzor (prayer book just for Yom Kippur) only has options for Monday, Wednesday, Thursday, and Saturday. And it made me think, how can they be so sure that Yom Kippur will never fall on a Sunday, Tuesday, or Friday? Thanks to this wonderful write-up, now I know: the Jewish calendar has a "business rule" that guarantees it!