Interval i1 = new Intervall(10.,4.);
        Interval i2 = new Intervall(2.,4.);

        Double x1 = 3.;
        Double x2 = 2.;

        // i1 + i2
        System.out.println("" + i1 + " + " + i2 + " = " + i1.add(i2));
        // i1 - i2
        System.out.println("" + i1 + " - " + i2 + " = " + i1.sub(i2));
        // i1 * i2
        System.out.println("" + i1 + " * " + i2 + " = " + i1.mul(i2));
        // i1 / i2
        System.out.println("" + i1 + " / " + i2 + " = " + i1.div(i2));

        // i1 + x1
        System.out.println("" + i1 + " + " + x1 + " = " + i1.add(x1));
        // i1 - x2
        System.out.println("" + i1 + " - " + x2 + " = " + i1.sub(x2));
        // i1 * x1
        System.out.println("" + i1 + " * " + x1 + " = " + i1.mul(x1));

        // x1 in i1
        System.out.println("" + x1 + " in " + i1 + "?  " + i1.in(x1));
        // x2 in i2
        System.out.println("" + x2 + " in " + i2 + "?  " + i2.in(x2));