tensor(list of Lists) produces something useless

Nobody has claimed this yet.

This is not good:
```
i1 : tensor({1,2,3},{4,5,6},{7,8,9})

o1 = {((1, 4), 7), ((1, 4), 8), ((1, 4), 9), ((1, 5), 7), ((1, 5), 8), ((1, 5), 9), ((1, 6), 7), ((1, 6), 8), ((1, 6), 9), ((2, 4), 7), ((2, 4), 8), ((2, 4), 9), ((2,
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
5), 7), ((2, 5), 8), ((2, 5), 9), ((2, 6), 7), ((2, 6), 8), ((2, 6), 9), ((3, 4), 7), ((3, 4), 8), ((3, 4), 9), ((3, 5), 7), ((3, 5), 8), ((3, 5), 9), ((3, 6),
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
7), ((3, 6), 8), ((3, 6), 9)}

o1 : List
```
What we should get, ideally, is triples of elements.

Relatedly, there should be a `List^**ZZ` that produces tuples of elements of a list.

Start with the tensor(list of Lists) example and the proposed List^**ZZ behavior; locate the existing tensor and list-power entry points. Determine how nested lists should produce triples rather than Cartesian products, and define the corresponding List^**ZZ result. Done when the example returns triples and the related operator has the requested behavior, with tests covering both.

Written by the indexing model from the issue text.