using System;

​

public class Program

{

    public static void Main()

    {

        Action<Base> baseAction = (Base b) => Console.WriteLine("Base: " + b);

        Action<Derived> derivedAction = baseAction;

        // Action<Base> baseAction2 = derivedAction; // Doesn't work because you could then call derivedAction(new Base()) which is wrong

        Action<Action<Derived>> derivedHigherOrderFunction = (Action<Derived> action) => {

            action(new Derived());

        };

        Action<Action<Base>> baseHigherOrderFunction = derivedHigherOrderFunction;

        baseHigherOrderFunction(baseAction);

    }

}

​

public class Base{}

​

public class Derived : Base{}