code: public static boolean isTipNode( LeftTupleNode node, TerminalNode removingTN ) {
          return NodeTypeEnums.isEndNode(node) || isNonTerminalTipNode( node, removingTN );
      }
docs: Returns whether the node is the tip of a segment.
  EndNodes (rtn and rian) are always the tip of a segment.
  
  node cannot be null.
  
  The result should discount any removingRule. That means it gives you the result as
  if the rule had already been removed from the network.