books.google.com - "Days, months, and years were given to us by nature, but we invented the week for ourselves. There is nothing inevitable about a seven-day cycle, or about any other kind of week; it represents an arbitrary rhythm imposed on our activities, unrelated to anything in the natural order. But where the week...https://books.google.com/books/about/The_Seven_Day_Circle.html?id=aGahKeojIUoC&utm_source=gb-gplus-shareThe Seven Day Circle
