title: is there a way to get only the nodes in the deepest layer?
body: <p>I have a graph with 'person' nodes, a basic relation of 'parent-child' between some nodes, and a transitive 'descendant' relation.</p>
  
  <p>for a specific 'person' I'd like get the oldest 'grandparents' the graph knows about ONLY.
  which means - they do not play the 'child' for any other node.</p>
  
  <p>what would be a good way to achieve that?</p>
  
  <p>thank you</p>