ILookup.cs

using System.Collections;
using System.Collections.Generic;

namespace System.Linq
{
    [global::__DynamicallyInvokable]
    public interface ILookup<TKey, TElement> : IEnumerable<IGrouping<TKey, TElement>>, IEnumerable
    {
        [global::__DynamicallyInvokable]
        int Count
        {
            [global::__DynamicallyInvokable]
            get;
        }

        [global::__DynamicallyInvokable]
        IEnumerable<TElement> this[TKey key]
        {
            [global::__DynamicallyInvokable]
            get;
        }

        [global::__DynamicallyInvokable]
        bool Contains(TKey key);
    }
}