My previous post (101 LINQ Samples) refers to very interesting samples. But I didn't pay attention that it is announcement as "future" features. So some of these samples aren't valid (were not implemented).
I'm not one found this trouble, in this forum thread shows what we can use instead of Fold (Aggregate) and EqualAll (SequenceEqual), we should use own realization according to situations for some other operations (SelectMany, Combine).
"Everybody lies" (c) House M.D.