To simplify a1 + a2 + ... + an, Maxima calls great O(n^2)
times. That's too many. I think simplus could make better use of
sorting to reduce the number of calls to great---you don't have to
change 'great' to do that. I suppose the speedup isn't comparable to
speed-up described in ``Experiments in Hash-coded Algebraic
Simplification.''
Barton