using System;

public class Program

{

    public static void Main()

    {

        Program p = null;

        Console.WriteLine(p is null); // correct

        Console.WriteLine(p == null); // wrong

    }

    public static bool operator ==(Program p1, Program p2)

    {

        return false;

    }

    public static bool operator !=(Program p1, Program p2)

    {

        return true;

    }

}