anchor.diff:      |> String.concat ", "
       |> sprintf "{%s}"
   
  -let inline private except(sequence: 'a seq, exceptSeq: 'a seq): 'a list =
  +let inline private except(baseSeq: 'a seq, exceptSeq: 'a seq): 'a list =
     let groupByOccurances sequence =
       sequence
       |> Seq.groupBy id
  
positive.code:                 (expected : _ seq)
                  format =
    let extra, missing =
      except(expected, actual),
      except(actual, expected)
  
    if List.isEmpty missing then () else
  
    sprintf "%s.
      Sequence `actual` does not contain all `expected` elements.
  
negative.code:       differNrOfElement element
      else Array.create (snd element) (fst element) |> Array.toList
    
    baseSeq
    |> groupByOccurances
    |> Seq.map elementsWhichDiffer
    |> List.concat
  