anchor.diff:  -include_lib("proper/include/proper.hrl").
   
   to_string({ident, Ident, _}) ->
  -    Ident;
  -to_string({symbol, Ident, _}) ->
  -    ":" ++ Ident;
  +    atom_to_list(Ident);
   to_string({quote, Value, _}) ->
      "'" ++ to_string(Value);
   to_string({fun_ref, {Module, Fun, Arity}, _}) ->
  
positive.code: compare({quote, Value1, _}, {quote, Value2, _}) ->
      compare(Value1, Value2);
  compare({vector, V1, _}, {vector, V2, _}) ->
      lists:all(fun({I1, I2}) ->
                        compare(I1, I2)
                end, lists:zip(V1, V2));
  
negative.code:     union([33,
             integer(35, 38),
             integer(42, 46),
             integer(60, 90),
             integer(94, 95),
             integer(97, 122),
             integer(126, 127)]).
  
  ident_character() ->
      union([33,
             integer(35, 38),
             integer(42, 46),
             integer(60, 90),
             integer(94, 122)]).
  
  ident_string() ->
      ?LET({S1, S2},
  