Comment by xigoi
2 days ago
> By direction, I mean that if you define "a grandparent is the parent of a parent", you can now use that rule not just to evaluate whether one person is a parent (or to find all grandparents) but also to conclude that if you know someone is a grandparent, and they are the parent of some one, then that person is someone's parent.
Not necessarily.
Could you please expand? Because I have the same state of knowledge of the previous poster. I would like to learn if I'm wrong.
Someone who is a grandparent may also have other children who do not have children.