The source of Seder Hishtalshelus (origin of the Kav) is an identifiable entity before Tzimzum. In essence, therefore, the Kav emerges, not as Yesh M’ayin, but rather from a state of Helem to one of Gilui—unlike the novel, transcendent Ohr elicited by the Avodah of the Eved Pashut.
