Efficient algorithms for simplification

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Hi! I come back on an issue on Sage/Maxima, about simplification. I have some large rational polynomial expressions in -say- ten variables that I would like to simplify. simplify() does not work properly: the expression still remains too long. simplify_rational() and simplify_full() are even worse, and too slow. My question is whether, at least for simplifying rational polynomial expression, you know any algorithm or trick that can be used. Thanks in advance!