> Einsteins notation (X_n Y^n being defined as sum over ‘n’ of X_n times Y^n) is one of the most elegant and simple solutions that really work. Yes, but that n

> Einsteins notation (X_n Y^n being defined as sum over ‘n’ of X_n times Y^n) is one of the most elegant and simple solutions that really work. Yes, but that notation still includes the indexes being summed over, which I think is the point that no. 7 was trying to make. What doesn't work is a notation that just says XY, without any indexes whatsoever. The ordering of indexes and the specification of which indexes are being summed over matters, so a notation that leaves those things out doesn't work.