code: protected boolean isEquivalentInTheSet(Node node, Set<Node> set)
  	{
  		return set.contains(node) ||
  			isEquivalentInTheSet(node, UPWARD, set) || isEquivalentInTheSet(node, DOWNWARD, set); 
  	}
docs: Checks if an equivalent of the given node is in the set.
  @param node Node to check equivalents
  @param set Node set
  @return true if an equivalent is in the set