anchor.diff:  
       /// Return the list corresponding to the remaining items in the sequence.
       /// Forces the evaluation of the first cell of the list if it is not already evaluated.
  +    [<CompiledName("Tail")>]
       let tail (list : LazyList<'T>) =
           match getCell list with
           | CellCons (_, tl) -> tl
  
positive.code: 
      /// Build a new collection whose elements are the results of applying the given function
      /// to the corresponding elements of the two collections pairwise.
      let rec map2 (mapping : 'T1 -> 'T2 -> 'U) (list1 : LazyList<'T1>) (list2 : LazyList<'T2>) =
          lzy <| fun () ->
              match getCell list1, getCell list2 with
  
negative.code:         loop [] list
  
      /// Apply the given function to each element of the collection.
      [<CompiledName("Iterate")>]
      let rec iter (action : 'T -> unit) (list : LazyList<'T>) =
          match getCell list with
          | CellEmpty -> ()
  