Right, changing the order would be a pain. Although if the reason for doing so is memory layout (for speed), then a lazy permutedims(A) would decouple index order from this. Perhaps when creating a tensor for the first time there ought to be a way to specify the layout? Haven't thought much but something like A[n^4, μ,ν, c^1] := .... would not be hard to do.

In your prod<2>(a, b, ... example, if p1 and p2 are in the same space, how would a*b know which one to contract? Or do they have different names from when a was created?