Dear All, Browsing email on my vacation I noticed a discussion on indexed objects. So far my impression is that GiNaC FAQ is mainly written in do-not-do-this-and-that style. Some active GiNaC users (e.g. me) may wish to see more positive suggestion. For example, I would be grateful for answering such questions: Q4. "Indices" of various kinds proved to be useful in different areas of mathematics, e.g. linear algebra. If present idx and varidx classes are strictly reserved for differential geometric usage in spaces with fractional dimensions, are there plans to add some other classes, say "labels", which may be freely utilised for other purposes? Q5. I need expressions of the type \sum_{j=1}^n a_j b_j for an unspecified symbolic value n and quantities a_j and b_j *labelled* (rememberring that _indexed_ is already copyrighted) by j in this range. Since the varidx class for j is not encouraged and the Einstein summing convention is not "meaningful" in GiNaC, what is the recommended way to define such a sum in my program? Best wishes from the sunny Odessa ;-) Vladimir -- Vladimir V. Kisil email: kisilv@maths.leeds.ac.uk