public static IAsyncEnumerable <TResult> GroupBy <TSource, TKey, TElement, TResult>(this IAsyncEnumerable <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector, Func <TKey, IAsyncEnumerable <TElement>, TResult> resultSelector, IEqualityComparer <TKey> comparer) =>
 LinqEnumerable.GroupBy(source, keySelector, elementSelector, resultSelector, comparer);
 public static IAsyncEnumerable <IAsyncGrouping <TKey, TSource> > GroupBy <TSource, TKey>(this IAsyncEnumerable <TSource> source, Func <TSource, TKey> keySelector, IEqualityComparer <TKey> comparer) =>
 LinqEnumerable.GroupBy(source, keySelector, comparer);
 public static IAsyncEnumerable <IAsyncGrouping <TKey, TElement> > GroupBy <TSource, TKey, TElement>(this IAsyncEnumerable <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector) =>
 LinqEnumerable.GroupBy(source, keySelector, elementSelector);
 public static IAsyncEnumerable <TResult> GroupBy <TSource, TKey, TResult>(this IAsyncEnumerable <TSource> source, Func <TSource, TKey> keySelector, Func <TKey, IAsyncEnumerable <TSource>, TResult> resultSelector) =>
 LinqEnumerable.GroupBy(source, keySelector, resultSelector);