anchor.diff:  delete(DB, Key, WriteOptions) ->
       call(DB, {?H2LDB_DELETE3, Key, WriteOptions}).
   
  --spec get(db(), key()) -> {ok, key()} | key_not_exist | {error, io_error}.
  +-spec get(db(), key()) -> {ok, value()} | key_not_exist | {error, io_error}.
   get(DB, Key) ->
       get(DB, Key, []).
   
   -spec get(db(), key(), [read_option()]) ->
  -                 {ok, key()} | key_not_exist | {error, io_error}.
  +                 {ok, value()} | key_not_exist | {error, io_error}.
   get(DB, Key, ReadOptions) ->
       call(DB, {?H2LDB_GET3, Key, ReadOptions}).
  -
   
   -spec put(db(), key(), value()) -> ok | {error, io_error}.
   put(DB, Key, Value) ->
  
positive.code:                       {ok, key()} | end_of_table | {error, io_error}.
  prev_key(DB, Key, ReadOptions) ->
      call(DB, {?H2LDB_PREV3, Key, ReadOptions}).
  
  
  %% ====================================================================
  
negative.code:          prev_key/3
          ]).
  
  -export([fold_keys/6,
           fold_keys/7,
           fold_kvs/6,
           fold_kvs/7
          ]).
  
  %% gen_server callbacks
  -export([init/1,
           handle_call/3,
  