using System;

public class Program

{

    public interface IA

    {

        string SomeProperty { get; set; }

    }

    public class A : IA

    {       

        public string SomeProperty { get; set; } = "non-initialized";

    }

    public class FakeAProxy : A, IA

    {

        string IA.SomeProperty

        {

            get => ActualState.SomeProperty;

            set => ActualState.SomeProperty = value;

        }

        internal A ActualState { get; set;} = new A { SomeProperty = "initialized" };

    }

    public static void Main()

    {

        var fakeProxy = new FakeAProxy();

        IA iProxy = fakeProxy;

        A aProxy = fakeProxy;

        Console.Write("fakeProxy.SomeProperty: ");

        Console.WriteLine(fakeProxy.SomeProperty);

        Console.Write("iProxy.SomeProperty: ");

        Console.WriteLine(iProxy.SomeProperty);

        Console.Write("aProxy.SomeProperty: ");

        Console.WriteLine(aProxy.SomeProperty);

    }

}