public class Plus extends BinOp {
  
    public Plus(Node left, Node right) {
	     super(left, right);
    }

    protected Double compute(Double d1, Double d2) {
       return d1 + d2;
    }

    public Node derive(String var) {
	      return new Plus(left.derive(var),right.derive(var))  ;    
    }
    
}