anchor.diff:           foreach/2,
            from_list/1,
            is_key/2,
  +         is_prefix/2,
            iter/2,
            itera/3,
            map/2,
  
positive.code: %% @end
  %%-------------------------------------------------------------------------
  
  update([H | T], _, Initial, {I0, I1, Data})
      when H < I0 ->
      NewData = erlang:setelement(1,
  
negative.code:     end;
  
  update([H | T] = Key, F, Initial, {I0, I1, Data})
      when is_integer(H), is_function(F, 1) ->
      I = H - I0 + 1,
      {Node, Value} = erlang:element(I, Data),
      case Node of
  