anchor.diff:  
   %% Utilities.
   
  -check(V1, V0) ->
  -    if V1 /= V0 ->
  -	    io:fwrite("error: ~w.\n", [V1]),
  -	    ?t:fail();
  -       true ->
  -	    io:fwrite("ok: ~w.\n", [V1])
  -    end.
  -
   echo(X) ->	    
       io:fwrite("eval(~w); ",[X]),
       X.
  
positive.code: 	     X andalso Y -> true;
  	     true -> false
  	 end,
      check(V1, X and Y).
  
  t_orelse_1({X,Y}) ->
      io:fwrite("~w orelse ~w: ",[X,Y]),
  
negative.code: 	     X orelse Y -> true;
  	     true -> false
  	 end,
      V1 = id(X or Y).
  
  inside(Config) when is_list(Config) ->
      ?line true = inside(-8, 1),
  