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();
      }
   }
//csharp/4821