LONDON (AP) — Here is one way to look at what Rafael Nadal, Novak Djokovic and the now-retired Roger Federer accomplished: The group known as the Big Three of men’s tennis accumulated so many Grand Slam titles — 63 in all — that it seems unlikely anyone will reach the standards they set. Not anytime soon, certainly. Here was another way to think about things as the professional level of the sport began its post-Federer life on Saturday, following the last match of his career: What he and the other two members of that distinguished trio, along with Serena Williams, managed to do was demonstrate that it is possible to dominate for decades, not merely years, at a time.