code: protected void initLowerEquivalent()
  	{
  		this.lowerEquivalent = new HashSet<Node>();
  
  		for (PhysicalEntity eq : pe.getMemberPhysicalEntity())
  		{
  			Node node = (Node) graph.getGraphObject(eq);
  			if (node != null) this.lowerEquivalent.add(node);
  		}
  
  		lowerEquivalentInited = true;
  	}
docs: Finds member nodes if this is a homology node