anchor.diff:  %% API.
   -export([start_link/0]).
   -export([get_user/2]).
  --export([user_shutting_down/1]).
  +-export([user_wants_to_shutdown/1]).
   
   %% gen_server.
   -export([init/1]).
  
positive.code: get_user(UserSubject, Issuer) ->
      load_or_return_user(#{ sub => UserSubject, iss => Issuer}).
  
  -spec user_shutting_down(ID :: binary()) -> ok.
  user_shutting_down(ID) ->
      gen_server:call(?MODULE,{delete_user,ID}).
  
  %% gen_server.
  
  
negative.code:     case add_new_user_entry(UserId,Pid) of
          ok -> 
              {ok, Pid};
          {error, already_exists} ->
              ok = tts_user:stop(Pid),
              lookup_user(UserMap)
      end.
  