PlainOldSum.cs

using System;

class Program
{
    static void Main()
    {
        Func<int, int, int> sum = (lhs, rhs) => lhs + rhs;
        Console.WriteLine(sum(1, 2)); // 3
        Console.WriteLine(sum(4, 5)); // 9

        Func<int, int> onePlus = rhs => sum(1, rhs);
        Console.WriteLine(onePlus(1)); // 2
        Console.WriteLine(onePlus(211)); // 212

        Func<int, int> twoPlus = rhs => sum(2, rhs);
        Console.WriteLine(twoPlus(1)); // 3
        Console.WriteLine(twoPlus(211)); // 213
    }
}