public static EnumerableExtensions.ValueEnumerable <ImmutableStack <TSource>, ValueEnumerator <TSource>, ImmutableStack <TSource> .Enumerator, TSource, GetEnumerator <TSource>, GetEnumerator2 <TSource> > AsValueEnumerable <TSource>(this ImmutableStack <TSource> source)
 => source.AsValueEnumerable <ImmutableStack <TSource>, ValueEnumerator <TSource>, ImmutableStack <TSource> .Enumerator, TSource, GetEnumerator <TSource>, GetEnumerator2 <TSource> >();