anchor.diff:  command(Pool, Command) ->
     command(Pool, Command, undefined).
   
  --spec command(pid(), bson:document(), readprefs()) -> {boolean(), bson:document()} | {error, reason()}. % Action
  +-spec command(map(), bson:document(), readprefs()) -> {boolean(), bson:document()} | {error, reason()}. % Action
   command(#{pool := Pool, server_type := ServerType, readPreference := RPrefs}, Command, Db) ->
     Q = #'query'{
       collection = {Db, <<"$cmd">>},
  
positive.code: -type reason() :: atom().
  
  
  
  -spec find(pid(), colldb(), mongo:selector()) -> mongo:cursor().
  -spec find(pid(), colldb(), mongo:selector(), readprefs()) -> mongo:cursor().
  
  
  %% @doc Creates new topology discoverer, return its pid
  -spec connect(seed(), connectoptions(), workeroptions()) -> {ok, Pid :: pid()} | ignore | {error, Reason :: term()}.
  connect(Seeds, Options, WorkerOptions) ->
  
negative.code:       Error
    end.
  
  -spec find_one(map(), colldb(), mongo:selector(), readprefs()) -> map().
  find_one(#{pool := Pool, server_type := ServerType, readPreference := RPrefs}, Coll, Selector, Options) ->
    Projector = mc_utils:get_value(projector, Options, []),
    Skip = mc_utils:get_value(skip, Options, 0),
  