public static bool Connected(IAirport a1, IAirport a2)
        {
            bool connected = false;

            foreach (IAirport airport in a1.GetAirports())
            {
                if (airport == a2)
                {
                    connected = true; break;
                }
            }
            return(connected);
        }
 public static void Connect(IAirport a1, IAirport a2) //povezujemo dva aerodroma tako sto ih dodamo medjusobno
 {                                                    //u listu njihovih povezanih aerodroma
     a1.GetAirports().Add(a2);
     a2.GetAirports().Add(a1);
 }