code: protected void initUpperEquivalent()
  	{
  		this.upperEquivalent = new HashSet<Node>();
  
  		for (PhysicalEntity eq : pe.getMemberPhysicalEntityOf())
  		{
  			Node node = (Node) graph.getGraphObject(eq);
  			if (node != null) this.upperEquivalent.add(node);
  		}
  
  		upperEquivalentInited = true;
  	}
docs: Finds homology parent.