# How to make formal variables with more than one index?

I'd like to make formal variables that can be multiplied, added etc. but have them labelled by two indices.

Here:
https://ask.sagemath.org/question/792...
it's done for variables with one index, and I asked a similar question about defining differential forms with multi-labels here:
https://ask.sagemath.org/question/468...
I see no clear way of merging these two approaches.