@Override
	public String toString(){
		String str = "";
		if(node1.getClass().equals(getClass()) || !(node1 instanceof Operation))
			str += node1.toString();
		else
			str += "(" + node1 + ")";
		str += super.toString();
		if(node2.getClass().equals(getClass()) || !(node2 instanceof Operation))
			str += node2.toString();
		else
			str += "(" + node2 + ")";
		return str;
	}