class PolynomialSplineFunction implements UnivariateDifferentiableFunction, DifferentiableUnivariateFunction {

    public boolean isValidPoint(double x) {
        if (x < knots[0] ||
            x > knots[n]) {
            return false;
        } else {
            return true;
        }
    }

    public  PolynomialSplineFunction(double knots[], PolynomialFunction polynomials[]);

}