anchor.diff:  
   %% verify using top-down BFS traversal
   
  +-spec verify_upper(tree()) -> boolean().
   verify_upper(Tree=#tree{height=Height}) ->
       verify(Height, Tree).
   
  +-spec verify(tree()) -> boolean().
   verify(Tree=#tree{height=Height}) ->
       verify(Height + 1, Tree).
   
  
positive.code: 
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  corrupt(Key, Tree=#tree{height=Height}) ->
      Segment = get_segment(Key, Tree),
      Bucket = {Height + 1, Segment},
  
negative.code:                  modstate=Mod:new(Opts)},
      reload_top_hash(Tree).
  
  -spec reload_top_hash(tree()) -> tree().
  reload_top_hash(Tree) ->
      {ok, TopHash} = m_fetch({0,0}, undefined, Tree),
      Tree#tree{top_hash=TopHash}.
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  -spec height(tree()) -> pos_integer().
  height(#tree{height=Height}) ->
      Height.
  
  -spec top_hash(tree()) -> hash() | undefined.
  top_hash(#tree{top_hash=TopHash}) ->
      TopHash.
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  -spec insert(key(), value(), tree()) -> tree() | corrupted().
  insert(Key, Value, Tree) when is_binary(Value) ->
      Segment = get_segment(Key, Tree),
      case get_path(Segment, Tree) of
  