Nadal and Federer will both stop at 20 GS, Djokovic will win at least 23 GS, plus 2 career grand slams, plus winning every single masters title twice, plus the most weeks at #1, plus Nole slam from 2015 Wimbledon - 2016 French Open, plus he has a winning head to head record against both Nadal and Federer, plus the most year end #1. Djokovic is no doubt the greatest tennis player of all time!