We learned in the Book of Mysteries that there is an upper Yud and a lower Yud, an upper Hei and a lower Hei, an upper Vav and a lower Vav. The upper letters derive from Atika and the lower are in Zeir Anpin. They do not derive from him but are truly in him. Zeir Anpin is called Yud Hei Vav Hei, and the inner meaning of the letters applies to him. As for Atika Kadisha, they merely derive from it; meaning, the roots of the four letters Yud Hei Vav Hei are in it, not the letters themselves. The name of Atika is hidden from everything, unattainable; but these letters Yud Hei Vav Hei derive from Atika to sustain these letters below. Without it, the lower letters would not endure.