Rabbi Yitzchak and Rabbi Yehudah, etc.: Rabbi Yitzchak and Rabbi Yehudah were sitting one night and studying the Torah. Rabbi Yitzchak said to Rabbi Yehudah: "We have already learned that when the Holy One, Blessed Be He, created the world, He made the lower world similar to the upper world, and made everything correspond, so that every part and detail in the lower world has its corresponding root in the upper world, and it is His honor above and below".