anchor.diff:  %% following code.
   -define(KNOWN_COMMANDS, #{<<"look">> => cmd_look,
                             <<"go">> => cmd_go,
  +                          <<"g">> => cmd_go,
                             <<"get">> => cmd_get,
                             <<"take">> => cmd_get,
                             <<"quit">> => cmd_quit,
  -                          <<"exit">> => cmd_exit}).
  +                          <<"exit">> => cmd_exit,
  +                          <<"help">> => cmd_help,
  +                          <<"h">> => cmd_help,
  +                          <<"?">> => cmd_help}).
   
   %% Initial locations of all objects in the game. Items in the
   %% inventory are marked by special location indicated by atom 'body'.
  
positive.code: move_to(NewLocation, #{edges := Edges} = State) ->
      State#{location := NewLocation, location_edges := maps:get(NewLocation, Edges)}.
  
  unlines(ListOfStrings) ->
      list_to_binary(string:join(ListOfStrings, "\n")).
  
  
negative.code:     maps:get(Location, Rooms).
  
  describe_directions(#{location_edges := Edges}) ->
      unlines(
        [ io_lib:format("There is a ~s going to ~s from there", [Direction, Room])
          || {Direction, Room} <- maps:to_list(Edges)
        ]).
  
  describe_objects(#{location := Location, objects := Objects}) ->
      ObjectsInCurrentLocation =
  