anchor.diff:  type time = System.DateTime
   let now () = System.DateTime.Now
   let time_diff (t1:time) (t2:time) : float * int =
  -    let ts = t2 - t1 in 
  +    let ts = t2 - t1 in
       ts.TotalSeconds, int32 ts.TotalMilliseconds
  -let record_time f = 
  +let record_time f =
       let start = now () in
  -    let res = f () in 
  +    let res = f () in
       let _, elapsed = time_diff start (now()) in
       res, elapsed
   let get_file_last_modification_time f = System.IO.File.GetLastWriteTime f
  
positive.code:   e.Message
  
  let format_md5 bytes =
    let sb = 
      Array.fold 
        (fun (acc:StringBuilder) (by:byte) ->
          acc.Append(by.ToString("x2")))
        (new StringBuilder())
  
negative.code:   | Inl of 'a
    | Inr of 'b
  
  let is_left = function
    | Inl _ -> true
    | _ -> false
  let is_right = function
  