gistfile1.cs

using System;
using N; // This using directive is unused, but cannot be simply removed

static class C
{
    static void Ex(this string x) { }
    static void Foo(Action<string> x, int y) { }
    static void Foo(Action<string> x, string y) { }
    static void Foo(Action<string> x, object y) { }
    static void Foo(Action<int> x, int y) { }
    static void Main()
    {
        Foo(y => Foo(x => x.Ex(), y), 0);
    }
}

namespace N
{
    static class E
    {
        public static void Ex(this int x) { }
    }
}