public static IAsyncEnumerable <TResult> GroupJoin <TOuter, TInner, TKey, TResult>(this IAsyncEnumerable <TOuter> outer, IAsyncEnumerable <TInner> inner, Func <TOuter, TKey> outerKeySelector, Func <TInner, TKey> innerKeySelector, Func <TOuter, IAsyncEnumerable <TInner>, TResult> resultSelector, IEqualityComparer <TKey> comparer) => LinqEnumerable.GroupJoin(outer, inner, outerKeySelector, innerKeySelector, resultSelector, comparer);