 On the face of it, what we mean in (4) is that if parents x and y had not existed, then their child z could not have come into existence. This looks like a case of rigid existential dependence, but it is clear that once z has been born, her parents can go out of existence without any effect on her own existence. At that point, there is only past rigid existential dependence. For cases such as this, we would require temporally relativized versions of  (EDN)  and  (EDG),  but we will omit these complications here (see Thomasson 1998: 24–34 and Correia 2005, 2008 for some versions of temporally relativized ontological dependence).