anchor.diff:          none ->
               % Look ahead.
               {SubtreeKeyNo, _, SubtreeKeyValues, _} = Subtree = lists:nth(SubtreePos, Subtrees),
  -            case SubtreeKeyNo == KeyNoMax of
  +            case SubtreeKeyNo of
                   % Split node.
  -                true ->
  +                KeyNoMax ->
                       {SplitKeyValues, SplitSubtrees1, SplitTree1, SplitTree2, SplitSubtrees2} = split_node_non_root(KeyNo, KeyValues, Subtrees, Subtree, SubtreePos, SubtreeNoMin, SortFunction, nil),
                       {
                           KeyNo + 1,
  
positive.code: % Leaf node.
  lookup_1(Key, {KeyNo, 0, KeyValues, []}, SortFunction, _) ->
      {Value, _} = binary_search(Key, KeyValues, KeyNo, 1, KeyNo, SortFunction),
      case Value == none of
          true ->
              Value;
          _ ->
              {value, Value}
  
negative.code: is_defined(_, {_, _, 0, _, _, nil}) ->
      false;
  is_defined(Key, {_, _, _, SortFunction, State, Tree}) ->
      case lookup_1(Key, Tree, SortFunction, State) of
          none ->
              false;
          _ ->
              true
  