// csc.exe /langversion:7 /t:library a.cs
public class A { }
public class B { public A F; }

// csc.exe /r:a.dll /t:library b.cs
class C
{
    static T F<T>(T x, T y) => x;
    static void G(A? x, B b)
    {
        var y = b.F;
        F(x, y).ToString();
        F(y, x).ToString();
    }
}