anchor.diff:          checkNonNull "map" map
   
           map.ToMap ()
  -
  +*)
       /// Searches the map looking for the first element where the given function
       /// returns a Some value. If no such element is found, returns None.
       [<CompiledName("TryPick")>]
  
positive.code:     /// Returns a new HashMap with the binding added to this HashMap.
      member this.Add (key : 'Key, value : 'T) : HashMap<'Key, 'T> =
          // If the trie isn't modified, just return this HashMap instead of creating a new one.
          let trie' = PatriciaHashMap.Add (key, value, trie)
          if trie === trie' then this
          else HashMap (trie')
  
      /// Returns a new HashMap with the binding added to this HashMap.
      member this.TryAdd (key : 'Key, value : 'T) : HashMap<'Key, 'T> =
          // If the trie isn't modified, just return this HashMap instead of creating a new one.
          let trie' = PatriciaHashMap.TryAdd (key, value, trie)
          if trie === trie' then this
          else HashMap (trie')
  
negative.code:             notSupported "HashMaps cannot be mutated."
  
          /// <inherit />
          member __.Contains (item : KeyValuePair<'Key, 'T>) =
              let keyHash = uint32 <| hash item.Key
              match PatriciaHashMap.TryFind (keyHash, item.Key, trie) with
              | None ->
                  false
              | Some value ->
  