This means that the diagonals are in that order, but does not affect the order of the items in each of the diagonals, although that does seem a bit ambiguous, so I'll probably remove that.

Made it order-dependent.

Added a picture showing the example in the question.

I have added a description of lattice multiplication in its section.

What if someone appended things in a different order? (Example: What if someone adding the items 3, 5, 6 to a list instead of 5, 3, 6?) I'm only sorting them to see whether they have the right items.

Marking issue as resolved.

done

That kata only wants you to find the indices, but this kata focuses more on creating the lists.

Solved it.

Thanks for your suggestions. I have updated it.

Is it working now? I forgot to publish the kata earlier.

I have also found a testcase where https://www.codewars.com/kata/reviews/63b06eebd78d850001cac165/groups/63b072a2cddb40000122f5cc doesn't pass

Uses updated test framework now.

Added random tests