Read Only ObservableCollection as contract interface

INotifyCollection.cs

public interface INotifyCollection<T> 
       : ICollection<T>, 
         INotifyCollectionChanged
{}

IReadOnlyNotifyCollection.cs

public interface IReadOnlyNotifyCollection<out T> 
       : IReadOnlyCollection<T>, 
         INotifyCollectionChanged
{}

NotifyCollection.cs

public class NotifyCollection<T> 
       : ObservableCollection<T>, 
         INotifyCollection<T>, 
         IReadOnlyNotifyCollection<T>
{}

Usage:

public class Program
{
    private static void Main(string[] args)
    {
        var full = new NotifyCollection<string>();
        var readOnlyAccess = (IReadOnlyCollection<string>) full;
        var readOnlyNotifyOfChange = (IReadOnlyNotifyCollection<string>) full;


        //Covarience
        var readOnlyListWithChanges = 
            new List<IReadOnlyNotifyCollection<object>>()
                {
                    new NotifyCollection<object>(),
                    new NotifyCollection<string>(),
                };
    }
}