Instructive for the study of the development of Jewish mysticism is the "Book of Jubilees" written around the time of King John Hyrcanus. It refers to mysterious writings of Jared, Cain, and Noah, and presents Abraham as the renewer, and Levi as the permanent guardian, of these ancient writings. It offers a cosmogony based upon the twenty-two letters of the Hebrew alphabet, and connected with Jewish chronology and Messianology, while at the same time insisting upon the heptad (7) as the holy number, rather than upon the decadic (10) system adopted by the later haggadists and observable in the "Sefer Yetzirah". The Pythagorean idea of the creative powers of numbers and letters was shared with "Sefer Yetzirah" and was known in the time of the Mishnah before 200 CE.