I'm not convinced yet, but I don't want to make this argument longer. It wasn't my intention to make you or anybody lose time (sorry if I did, truly!), I just thought you were pointing something that failed to be true and that I could correct you in a friendly manneer. Your comment is interesting and I'll think about it, but as far as I could see it seems to work only in particular cases and not in all negative cases, as you had pointed before. But I need to think more about it to be sure. Thanks for your time and for your explainations.