case Alternative(Tree[] ts):
case Alternative(_):
    public void traverse(Tree tree) {    	if (!result)			switch (tree) {				case Alternative(Tree[] ts):					result = true;					break;				case Bind(_, Tree pat):					variables.add(tree.symbol());					traverse(pat);					break;				case Ident(_):					if (variables.contains(tree.symbol()))						result = true;					break;				default:					super.traverse( tree );			}    }