public static ReadOnlyList.SelectManyEnumerable <ImmutableList <TSource>, TSource, TSubEnumerable, TSubEnumerator, TResult> SelectMany <TSource, TSubEnumerable, TSubEnumerator, TResult>(
this ImmutableList <TSource> source,
Selector <TSource, TSubEnumerable> selector)
where TSubEnumerable : notnull, IValueEnumerable <TResult, TSubEnumerator>
where TSubEnumerator : struct, IEnumerator <TResult>
=> ReadOnlyList.SelectMany <ImmutableList <TSource>, TSource, TSubEnumerable, TSubEnumerator, TResult>(source, selector);