class CombinedCurve implements Curve, ImmutableBean, Serializable {

  @Override
  public double firstDerivative(double x) {
    return baseCurve.firstDerivative(x) + spreadCurve.firstDerivative(x);
  }

  @ImmutableConstructor private  CombinedCurve(
      Curve baseCurve,
      Curve spreadCurve,
      CurveMetadata metadata);

}