anchor.diff:              Br (p, m, t1, t0)
   
       /// Insert a binding (key-value pair) into a map, returning a new, updated map.
  -    static member Insert (key, value : 'T, map) =
  +    static member TryAdd (key, value : 'T, map) =
           match map with
           | Empty ->
               Lf (key, value)
  
positive.code: 
          (Empty, source)
          ||> Map.fold (fun trie key value ->
              PatriciaMap.Insert (uint32 key, value, trie))
  
      //
      member this.Iterate (action : int -> 'T -> unit) : unit =
  
negative.code:     /// Returns a new IntMap with the binding added to this IntMap.
      member __.Add (key : int, value : 'T) : IntMap<'T> =
          IntMap (
              PatriciaMap.Add (uint32 key, value, trie))
  
      /// Returns a new IntMap with the binding added to this IntMap.
      member this.TryAdd (key : int, value : 'T) : IntMap<'T> =
          // If the tree wasn't modified, return the reference to this IntMap
          // instead of creating a new one.
          let trie' = PatriciaMap.TryAdd (uint32 key, value, trie)
          if trie === trie' then
              this
          else
              IntMap (trie')
  
      /// Removes an element from the domain of the IntMap.
      /// No exception is raised if the element is not present.
  