using System;

public class Program

{

    public static void Main()

    {

        try

        {

            Parent parent = new Parent{ Name = "Parent" };

            One(parent);

        }

        catch (Exception e)

        {

            Console.WriteLine(e.Message);           

        }

        try

        {

            Child child = new Child{ Name = "Child" };

            One(child);

        }

        catch (Exception e)

        {

            Console.WriteLine(e.Message);           

        }

    }

    public static void One(Parent parent)

    {

        Console.WriteLine(parent.Name + ":");

        if (parent is Child child)

        {

            Console.WriteLine(parent.Name + " is a child");

        }

        Two(parent);

    }

    public static void Two(Parent parent)

    {

        Console.WriteLine("Two/Parent: " + parent.Name);

​

        if (parent is Child child)

        {

            Console.WriteLine(parent.Name + " is a child");

        }

​

        Two(parent as Child);

    }

​

    public static void Two(Child child)

    {

        Console.WriteLine("Two/Child: " + child.Name);

        Three(child);

    }

​

    public static void Three(Parent parent)

    {

        Console.WriteLine("Three: " + parent.Name);

​

        if (parent is Child child)

        {

            Console.WriteLine(parent.Name + " is a child");

        }

    }

}

​

public class Parent

{

    public string Name;

}

​

public class Child : Parent

{

    public int Age;

}