anchor.diff:  % Non-Leaf node.
   lookup_1(Key, {KeyNo, _, KeyValues, Subtrees}, SortFunction, nil) ->
       {Value, Pos} = binary_search(Key, KeyValues, KeyNo, 1, KeyNo, SortFunction),
  -    case Value == none of
  -        true ->
  +    case Value of
  +        none ->
               lookup_1(Key, lists:nth(Pos, Subtrees), SortFunction, nil);
           _ ->
               {value, Value}
       end;
   lookup_1(Key, {KeyNo, _, KeyValues, SubtreesKey}, SortFunction, {StateTarget, _, _, LookupFunction} = State) ->
       {Value, Pos} = binary_search(Key, KeyValues, KeyNo, 1, KeyNo, SortFunction),
  -    case Value == none of
  -        true ->
  +    case Value of
  +        none ->
               lookup_1(Key, lists:nth(Pos, LookupFunction(StateTarget, lookup, SubtreesKey)), SortFunction, State);
           _ ->
               {value, Value}
  
positive.code:                                                                               lists:nth(KeyPos - 1, Subtrees)
                                                                        end,
      {KeyNoXC, SubtreeNoXC, KeyValuesXC, SubtreesXC} = TreeXC = lists:nth(KeyPos, Subtrees),
      {KeyNoXCRight, SubtreeNoXCRight, KeyValuesXCRight, SubtreesXCRight} = case KeyPos == SubtreeNo of
                                                                                true ->
                                                                                    {0, 0, [], []};
                                                                                _ ->
                                                                                    lists:nth(KeyPos + 1, Subtrees)
  
negative.code:     SubtreesXCLeft = LookupFunction(StateTarget, lookup, SubtreesKeyXCLeft),
      {KeyNoXC, SubtreeNoXC, KeyValuesXC, SubtreesKeyXC} = TreeXC = lists:nth(KeyPos, Subtrees),
      SubtreesXC = LookupFunction(StateTarget, lookup, SubtreesKeyXC),
      {KeyNoXCRight, SubtreeNoXCRight, KeyValuesXCRight, SubtreesKeyXCRight} = case KeyPos of
                                                                                   SubtreeNo ->
                                                                                       {0, 0, [], []};
                                                                                   _ ->
                                                                                       lists:nth(KeyPos + 1, Subtrees)
  