namespace System.Collections.Immutable
{
    public interface IImmutableDictionary<TKey, TValue> : IEnumerable, IEnumerable<KeyValuePair<TKey, TValue>>, IReadOnlyCollection<KeyValuePair<TKey, TValue>>, IReadOnlyDictionary<TKey, TValue>
    {
        IImmutableDictionary<TKey, TValue> Add(TKey key, TValue value);
    }
}