public static ValueTask <ILookup <TKey, TElement> > ToLookupAsync <TSource, TKey, TElement>(this IAsyncEnumerable <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector, IEqualityComparer <TKey> comparer) =>
 LinqEnumerable.ToLookupAsync(source, keySelector, elementSelector, comparer);
 public static ValueTask <ILookup <TKey, TSource> > ToLookupAsync <TSource, TKey>(this IAsyncEnumerable <TSource> source, Func <TSource, TKey> keySelector) =>
 LinqEnumerable.ToLookupAsync(source, keySelector);