anchor.diff:          Err -> Err
       end. 
   
  +handle_fib_command(Arg) ->
  +    case try_parse_int(Arg) of
  +        {ok, Int} when Int < 100 -> F = fib(Int), {ok, io_lib:format("~p", [F])};
  +        {ok, _Int} -> {error, floodgate};
  +        Err -> Err
  +    end.
  +
   handle_fac_command(Arg) ->
       case try_parse_int(Arg) of
           {ok, Int} when Int < 101 -> F = fac(Int), {ok, integer_to_list(F)};
  
positive.code:     case Tokens of
          ["fac", Arg] -> 
              H = handle_fac_command,
              MFA = {Mod, H, [Arg]},
              apply_command(From, To, MFA);
          ["fmt", Fmt, Arg] ->
  
negative.code:     end.
  
  fac(0) -> 1;
  fac(N) -> N * fac(N - 1).
  
  fib(0) -> 1;
  fib(1) -> 1;
  fib(N) -> fib(N - 2) + fib(N - 1).