using System;

using System.Collections.Generic;

using System.Linq;

​

namespace Tester

{

    public static class MyEnumerableExtensions

    {

        public static IEnumerable<IGrouping<TKey, TSource>> MyGroupBy<TSource, TKey>(

            this IEnumerable<TSource> source,

            Func<TSource, TKey> keySelector,

            IEqualityComparer<TKey> comparer)

        {

            throw new NotImplementedException();

        }

    }

}