How to implement ICollection and ISourceList

MySourceList.cs

    public class MySourceList<T>: ISourceList<T>, ICollection<T>
    {
        private readonly ISourceList<T> _innerList;

        public MySourceList()
        {
            _innerList = new SourceList<T>();
        }

        public int Count => _innerList.Count;
 

        public IObservable<int> CountChanged => _innerList.CountChanged;

        public IEnumerable<T> Items => _innerList.Items;

        public IObservable<IChangeSet<T>> Connect(Func<T, bool>? predicate = null) => _innerList.Connect(predicate);

        public IObservable<IChangeSet<T>> Preview(Func<T, bool>? predicate = null) => _innerList.Preview(predicate);

        public void Edit(Action<IExtendedList<T>> updateAction) => _innerList.Edit(updateAction);
        
        public void Dispose() => _innerList.Dispose();


        public void Add(T item) => _innerList.Add(item);

        public void Clear() => _innerList.Clear();

        public bool Contains(T item) => throw new NotImplementedException();

        public void CopyTo(T[] array, int arrayIndex) => throw new NotImplementedException();

        public bool Remove(T item) => _innerList.Remove(item);
        public bool IsReadOnly => false;


        public IEnumerator<T> GetEnumerator() => _innerList.Items.GetEnumerator();

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }