anchor.diff:      //
       member __.Iterate (action : int -> 'T -> unit) : unit =
           trie.Iterate action
  +
  +    //
  +    member __.IterateBack (action : int -> 'T -> unit) : unit =
  +        trie.IterateBack action
  +
  +    //
  +    member __.Fold (folder : 'State -> int -> 'T -> 'State, state : 'State) : 'State =
  +        trie.Fold (folder, state)
  +
  +    //
  +    member __.FoldBack (folder : int -> 'T -> 'State -> 'State, state : 'State) : 'State =
  +        trie.FoldBack (folder, state)
   
   //
   and [<Sealed>]
  
positive.code:         map.ToArray ()
  
      //
      let inline iter (action : int -> 'T -> unit) (map : IntMap<'T>) =
          // Preconditions
          checkNonNull "map" map
  
          map.Iterate action
  
  
      // TODO
  
negative.code:     // exists
      // filter
      // findKey
      // map
      // partition
      // pick
      // toSeq
      // tryFindKey
      // tryPick
  