public class Plane {
   public virtual double TopSpeed() { return 300.0D;}
   public static bool operator>(Plane one, Plane two) {  
     return one.TopSpeed() > two.TopSpeed();
   }
   public static bool operator<(Plane one, Plane two) {  
     return one.TopSpeed() < two.TopSpeed();
   }
  }
  class Jet : Plane {
   public override double TopSpeed() { return 900.0D; }
   public override string ToString() { return "I'm a Jet"; }
  }
   class Airport {
   [STAThread]
   static void Main(string[] args) {
     Plane plane = new Jet();
     Console.WriteLine("plane's top speed: {0}",plane.TopSpeed());
     Jet jet = new Jet();
     Console.WriteLine("jet's top speed: {0}",jet.TopSpeed());
     Console.WriteLine("Plane > Jet = {0}", plane > jet);
     Console.ReadLine();
   }
  }