public class ZweiK
        {
            public double x = 2.9;
            public double y = 2.8;

            public ZweiK() : this(0, 0) { }

            public ZweiK(double px, double py)
            {
                x = px;
                y = py;
            }
        }

        public class Vektor2D : ZweiK
        {
            public Vektor2D(double x, double y) : base(x, y) { }

            public static Vektor2D operator +(Vektor2D v1, Vektor2D v2)
            {
                return new Vektor2D(v1.x + v2.y, v1.y + v2.y);
            }

            public static Vektor2D operator -(Vektor2D v1, Vektor2D v2)
            {
                return new Vektor2D(v1.x - v2.x, v1.y - v2.y);
            }

            public static Vektor2D operator +(Vektor2D v)
            {
                return new Vektor2D(v.x, v.y);
            }

            public static Vektor2D operator -(Vektor2D v)
            {
                return new Vektor2D(-v.x, -v.y);
            }
        }