anchor.diff:          // Return the original map.
           map
   
  +/// <summary>
   /// Like Map.add, but only overwrites the value of an existing entry.
  -/// If the map does not contain the given key, KeyNotFoundException is raised.
  +/// If the map does not contain the given key, <see cref="KeyNotFoundException"/> is raised.
  +/// </summary>
  +/// <param name="key"></param>
  +/// <param name="value"></param>
  +/// <param name="map"></param>
  +/// <returns></returns>
   [<CompiledName("Update")>]
   let update key value (map : Map<'Key, 'T>) : Map<'Key, 'T> =
       // Preconditions
  
positive.code:             // Add/update the key-set for this value in the pivot map.
              Map.add value keySet pivotMap)
  
  /// Like Map.add, but doesn't overwrite an existing entry.
  [<CompiledName("TryAdd")>]
  let tryAdd key value (map : Map<'Key, 'T>) : Map<'Key, 'T> =
      // Preconditions
  
negative.code:     else
          keyNotFound "The map does not contain the specified key."
  
  /// <summary>Returns the number of map elements matching a given predicate.</summary>
  /// <param name="predicate"></param>
  /// <param name="map"></param>
  /// <returns></returns>
  /// <remarks><c>Map.countWith predicate map = (Map.filter predicate map |> Map.count)</c></remarks>
  [<CompiledName("CountWith")>]
  let countWith (predicate : 'Key -> 'T -> bool) (map : Map<'Key, 'T>) : int =
      // Preconditions
  